INSR-related severe syndromic insulin resistance comprises a phenotypic spectrum that is a continuum from the severe phenotype Donohue syndrome (DS) (also known as leprechaunism) to the milder phenotype Rabson-Mendenhall syndrome (RMS). DS at the severe end of the spectrum is characterized by severe insulin resistance (hyperinsulinemia with associated fasting hypoglycemia and postprandial hyperglycemia), severe prenatal growth restriction and postnatal growth failure, hypotonia and developmental delay, characteristic facies, and organomegaly involving heart, kidneys, liver, spleen, and ovaries. Death usually occurs before age one year. RMS at the milder end of the spectrum is characterized by severe insulin resistance that, although not as severe as that of DS, is nonetheless accompanied by fluctuations in blood glucose levels, diabetic ketoacidosis, and – in the second decade – microvascular complications. Findings can range from severe growth delay and intellectual disability to normal growth and development. Facial features can be milder than those of DS. Complications of longstanding hyperglycemia are the most common cause of death. While death usually occurs in the second decade, some affected individuals live longer.

Neonatal hemochromatosis (NH) is characterized by hepatic failure in the newborn period and heavy iron staining in the liver. In addition, there is marked siderosis of extrahepatic tissues, including the heart and pancreas (Driscoll et al., 1988). Whitington (2007) postulated that some cases of neonatal hemochromatosis result from maternal alloimmunity directed at the fetal liver, and therefore do not represent an inherited mendelian disorder. Other causes may result from metabolic disease or perinatal infection. In particular, he commented that the disorder is not related to the family of inherited liver diseases that fall under the classification of hereditary hemochromatosis (see, e.g., 235200). Whitington (2007) proposed the term 'congenital alloimmune hepatitis.' In the past, the disorder has loosely been labeled 'neonatal hepatitis' and 'giant cell hepatitis,' which are pathologic findings in the liver representing a common response to a variety of insults, including cholestatic disorders and infection, among others (Fawaz et al., 1975; Knisely et al., 1987; Kelly et al., 2001).

Systemic amyloidosis is a rare protein misfolding and deposition disorder caused by extracellular deposition of amyloid and leading to progressive organ failure. Amyloid is composed of highly organized proteinaceous, insoluble, and degradation-resistant fibrils. Hereditary systemic amyloidosis-2 (AMYLD2), resulting from mutation in the FGA gene, is the most common form of hereditary renal amyloidosis. The kidneys are the major affected organ, presenting with proteinuria. Other less frequently involved organs include liver, heart, autonomic nerve, and, rarely, peripheral nerve. A strong family history of coronary or vascular disease is also frequently seen (summary by Muchtar et al., 2021). The various forms of hereditary systemic amyloidosis that do not have peripheral neuropathy as part of the clinical syndrome have been referred to as 'Ostertag type' in reference to a German family described by Benno Ostertag (1932) in which several members died with renal amyloidosis. Since the form of hereditary amyloidosis caused by mutation in the FGA gene is the most common in Europe and has a clinical presentation with hypertension and proteinuria, Benson (2005) considered it a very good candidate for being the original amyloidosis described by Ostertag. For a discussion of genetic heterogeneity of hereditary systemic amyloidosis, see AMYLD1 (105210).

Arginase deficiency in untreated individuals is characterized by episodic hyperammonemia of variable degree that is infrequently severe enough to be life threatening or to cause death. Most commonly, birth and early childhood are normal. Untreated individuals have slowing of linear growth at age one to three years, followed by development of spasticity, plateauing of cognitive development, and subsequent loss of developmental milestones. If untreated, arginase deficiency usually progresses to severe spasticity, loss of ambulation, complete loss of bowel and bladder control, and severe intellectual disability. Seizures are common and are usually controlled easily. Individuals treated from birth, either as a result of newborn screening or having an affected older sib, appear to have minimal symptoms.

Congenital isolated adrenocorticotropic hormone deficiency (IAD) is characterized by severe hypoglycemia in the neonatal period, associated with seizures in about half of cases, prolonged cholestatic jaundice, and very low plasma ACTH levels with no significant response to corticotropin-releasing hormone (CRH; 122560). Plasma cortisol levels are also extremely low (Vallette-Kasic et al., 2005). TBX19 is required for initiation of transcription of the POMC gene (176830), which produces the precursor peptide from which ACTH is derived (Lamolet et al., 2001).

D-bifunctional protein deficiency is a disorder of peroxisomal fatty acid beta-oxidation. See also peroxisomal acyl-CoA oxidase deficiency (264470), caused by mutation in the ACOX1 gene (609751) on chromosome 17q25. The clinical manifestations of these 2 deficiencies are similar to those of disorders of peroxisomal assembly, including X-linked adrenoleukodystrophy (ALD; 300100), Zellweger cerebrohepatorenal syndrome (see 214100) and neonatal adrenoleukodystrophy (NALD; see 601539) (Watkins et al., 1995). DBP deficiency has been classified into 3 subtypes depending upon the deficient enzyme activity. Type I is a deficiency of both 2-enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase; type II is a deficiency of hydratase activity alone; and type III is a deficiency of dehydrogenase activity alone. Virtually all patients with types I, II, and III have a severe phenotype characterized by infantile-onset of hypotonia, seizures, and abnormal facial features, and most die before age 2 years. McMillan et al. (2012) proposed a type IV deficiency on the basis of less severe features; these patients have a phenotype reminiscent of Perrault syndrome (PRLTS1; 233400). Pierce et al. (2010) noted that Perrault syndrome and DBP deficiency overlap clinically and suggested that DBP deficiency may be underdiagnosed.

An autoimmune disorder characterized by the association of primary biliary cirrhosis with limited cutaneous systemic sclerosis. Onset occurs between 30-65 years. Occurs sporadically, but rare familial cases with an unknown inheritance pattern have been observed. There is no cure and management is mainly supportive.

MED12-related disorders include the phenotypes of FG syndrome type 1 (FGS1), Lujan syndrome (LS), X-linked Ohdo syndrome (XLOS), Hardikar syndrome (HS), and nonspecific intellectual disability (NSID). FGS1 and LS share the clinical findings of cognitive impairment, hypotonia, and abnormalities of the corpus callosum. FGS1 is further characterized by absolute or relative macrocephaly, tall forehead, downslanted palpebral fissures, small and simple ears, constipation and/or anal anomalies, broad thumbs and halluces, and characteristic behavior. LS is further characterized by large head, tall thin body habitus, long thin face, prominent nasal bridge, high narrow palate, and short philtrum. Carrier females in families with FGS1 and LS are typically unaffected. XLOS is characterized by intellectual disability, blepharophimosis, and facial coarsening. HS has been described in females with cleft lip and/or cleft palate, biliary and liver anomalies, intestinal malrotation, pigmentary retinopathy, and coarctation of the aorta. Developmental and cognitive concerns have not been reported in females with HS. Pathogenic variants in MED12 have been reported in an increasing number of males and females with NSID, with affected individuals often having clinical features identified in other MED12-related disorders.

MEDNIK syndrome is a severe multisystem disorder characterized by impaired intellectual development, enteropathy, deafness, peripheral neuropathy, ichthyosis, and keratoderma (summary by Montpetit et al., 2008). Patients with MEDNIK exhibit distinct dysmorphic features, including high forehead, upslanting palpebral fissures, depressed nasal bridge, and low-set ears, as well as growth retardation and moderate to severe intellectual disability, with brain atrophy on imaging. Other features include sensorineural deafness, enteropathy with congenital diarrhea, abnormalities of copper metabolism associated with liver disease, and ichthyosis, hyperkeratosis, and erythroderma. Peripheral neuropathy has also been observed in adult patients (Martinelli et al., 2013). MEDNIK syndrome shows phenotypic similarities to CEDNIK syndrome (609528).

Combined oxidative phosphorylation deficiency is an autosomal recessive multisystem disorder with variable manifestations resulting from a defect in the mitochondrial oxidative phosphorylation (OXPHOS) system. Onset occurs at or soon after birth, and features can include growth retardation, microcephaly, hypertonicity, axial hypotonia, encephalopathy, cardiomyopathy, and liver dysfunction. Death usually occurs in the first weeks or years of life (summary by Smits et al., 2011). Genetic Heterogeneity of Combined Oxidative Phosphorylation Deficiency See also COXPD2 (610498), caused by mutation in the MRPS16 gene (609204) on 10q22; COXPD3 (610505), caused by mutation in the TSFM gene (604723) on 12q14; COXPD4 (610678), caused by mutation in the TUFM gene (602389) on 16p11; COXPD5 (611719), caused by mutation in the MRPS22 gene (605810) on 3q23; COXPD6 (300816), caused by mutation in the AIFM1 gene (300169) on Xq26; COXPD7 (613559), caused by mutation in the MTRFR gene (613541) on 12q24; COXPD8 (614096), caused by mutation in the AARS2 gene (612035) on 6p21; COXPD9 (614582), caused by mutation in the MRPL3 gene (607118) on 3q22; COXPD10 (614702), caused by mutation in the MTO1 gene (614667) on 6q13; COXPD11 (614922), caused by mutation in the RMND1 gene (614917) on 6q25; COXPD12 (614924), caused by mutation in the EARS2 gene (612799) on 16p13; COXPD13 (614932), caused by mutation in the PNPT1 gene (610316) on 2p16; COXPD14 (614946), caused by mutation in the FARS2 gene (611592) on 6p25; COXPD15 (614947), caused by mutation in the MTFMT gene (611766) on 15q; COXPD16 (615395), caused by mutation in the MRPL44 gene (611849) on 2q36; COXPD17 (615440), caused by mutation in the ELAC2 gene (605367) on 17p11; COXPD18 (615578), caused by mutation in the SFXN4 gene (615564) on 10q26; COXPD19 (615595), caused by mutation in the LYRM4 gene (613311) on 6p25; COXPD20 (615917), caused by mutation in the VARS2 gene (612802) on 6p21; COXPD21 (615918), caused by mutation in the TARS2 gene (612805) on 1q21; COXPD22 (616045), caused by mutation in the ATP5A1 gene (164360) on 18q12; COXPD23 (616198), caused by mutation in the GTPBP3 (608536) gene on 19p13; COXPD24 (616239), caused by mutation in the NARS2 gene (612803) on 11q14; COXPD25 (616430), caused by mutation in the MARS2 gene (609728) on 2q33; COXPD26 (616539), caused by mutation in the TRMT5 gene (611023) on 14q23; COXPD27 (616672), caused by mutation in the CARS2 gene (612800) on 13q34; COXPD28 (616794), caused by mutation in the SLC25A26 gene (611037) on 3p14; COXPD29 (616811), caused by mutation in the TXN2 gene (609063) on 22q12; COXPD30 (616974), caused by mutation in the TRMT10C gene (615423) on 3q12; and COXPD31 (617228), caused by mutation in the MIPEP gene (602241) on 13q12; COXPD32 (617664), caused by mutation in the MRPS34 gene (611994) on 16q13; COXPD33 (617713), caused by mutation in the C1QBP gene (601269) on 17p13; and COXPD34 (617872), caused by mutation in the MRPS7 gene (611974) on 17q25; COXPD35 (617873), caused by mutation in the TRIT1 gene (617840) on 1p34; COXPD36 (617950), caused by mutation in the MRPS2 gene (611971) on 9q34; COXPD37 (618329), caused by mutation in the MICOS13 gene (616658) on 19p13; COXPD38 (618378), caused by mutation in the MRPS14 gene (611978) on 1q23; COXPD39 (618397), caused by mutation in the GFM2 gene (606544) on 5q13; COXPD40 (618835), caused by mutation in the QRSL1 gene (617209) on 6q21; COXPD41 (618838), caused by mutation in the GATB gene (603645) on 4q31; COXPD42 (618839), caused by mutation in the GATC gene (617210) on 12q24; COXPD43 (618851), caused by mutation in the TIMM22 gene (607251) on 17p13; COXPD44 (618855), caused by mutation in the FASTKD2 gene (612322) on 2q33; COXPD45 (618951), caused by mutation in the MRPL12 gene (602375) on 17q25; COXPD46 (618952), caused by mutation in the MRPS23 gene (611985) on 17q22; COXPD47 (618958), caused by mutation in the MRPS28 gene (611990) on 8q21; COXPD48 (619012), caused by mutation in the NSUN3 gene (617491) on 3q11; COXPD49 (619024), caused by mutation in the MIEF2 gene (615498) on 17p11; COXPD50 (619025), caused by mutation in the MRPS25 gene (611987) on 3p25; COXPD51 (619057), caused by mutation in the PTCD3 gene (614918) on 2p11; COXPD52 (619386), caused by mutation in the NFS1 gene (603485) on 20q11; COXPD53 (619423), caused by mutation in the C2ORF69 gene (619219) on 2q33; and COXPD54 (619737), caused by mutation in the PRORP gene (609947) on 14q13.; COXPD55 (619743), caused by mutation in the POLRMT gene (601778) on 19p13; COXPD56 (620139), caused by mutation in the TAMM41 gene (614948) on 3p25; COXPD57 (620167), caused by mutation in the CRLS1 gene (608188) on 20p12; COXPD58 (620451), caused by mutation in the TEFM gene (616422) on 17q11; and COXPD59 (620646), caused by mutation in the MRPL39 gene (611845) on 21q21.

Ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC) is a rare autosomal recessive syndrome characterized by scalp hypotrichosis, scarring alopecia, ichthyosis, and sclerosing cholangitis (summary by Feldmeyer et al., 2006).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500).

MPV17-related mitochondrial DNA (mtDNA) maintenance defect presents in the vast majority of affected individuals as an early-onset encephalohepatopathic (hepatocerebral) disease that is typically associated with mtDNA depletion, particularly in the liver. A later-onset neuromyopathic disease characterized by myopathy and neuropathy, and associated with multiple mtDNA deletions in muscle, has also rarely been described. MPV17-related mtDNA maintenance defect, encephalohepatopathic form is characterized by: Hepatic manifestations (liver dysfunction that typically progresses to liver failure, cholestasis, hepatomegaly, and steatosis); Neurologic involvement (developmental delay, hypotonia, microcephaly, and motor and sensory peripheral neuropathy); Gastrointestinal manifestations (gastrointestinal dysmotility, feeding difficulties, and failure to thrive); and Metabolic derangements (lactic acidosis and hypoglycemia). Less frequent manifestations include renal tubulopathy, nephrocalcinosis, and hypoparathyroidism. Progressive liver disease often leads to death in infancy or early childhood. Hepatocellular carcinoma has been reported.

Alagille syndrome (ALGS) is a multisystem disorder with a wide spectrum of clinical variability; this variability is seen even among individuals from the same family. The major clinical manifestations of ALGS are bile duct paucity on liver biopsy, cholestasis, congenital cardiac defects (primarily involving the pulmonary arteries), butterfly vertebrae, ophthalmologic abnormalities (most commonly posterior embryotoxon), and characteristic facial features. Renal abnormalities, growth failure, developmental delays, splenomegaly, and vascular abnormalities may also occur.

Neonatal diabetes mellitus with congenital hypothyroidism (NDH) syndrome is characterized by intrauterine growth retardation and onset of nonimmune diabetes mellitus within the first few weeks of life. Other features include renal parenchymal disease, primarily renal cystic dysplasia, and hepatic disease, with hepatitis in some patients and hepatic fibrosis and cirrhosis in others. Facial dysmorphism, when present, consistently involves low-set ears, epicanthal folds, flat nasal bridge, long philtrum, and thin upper lip. Most patients exhibit developmental delay (Dimitri et al., 2015).

Early-onset obesity with adrenal insuficiency and red hair (OBAIRH) is an autosomal recessive endocrine disorder characterized by early-onset obesity due to severe hyperphagia, pigmentary abnormalities, mainly pale skin and red hair, and secondary hypocortisolism. In the neonatal period, affected individuals are prone to hypoglycemia, hyperbilirubinemia, and cholestasis that may result in death if not treated. The disorder results from mutation in the POMC gene, which encodes a preproprotein that is processed into a range of bioactive peptides, including alpha-melanocyte-stimulating hormone (MSH) and ACTH (summary by Kuhnen et al., 2016 and Clement et al., 2008).

GRACILE syndrome is an autosomal recessive lethal disorder characterized by fetal growth retardation, lactic acidosis, aminoaciduria, cholestasis, and abnormalities in iron metabolism. Patients develop fulminant lactic acidosis during the first day of life. Despite intensive care, about half of affected infants die during the first days of life, and the remainder within 4 months of life. Finnish and British patients have been reported, with slightly different phenotypes; the British patients have additional features of complex III deficiency and neurologic symptoms (Visapaa et al., 2002).

Alagille syndrome (ALGS) is a multisystem disorder with a wide spectrum of clinical variability; this variability is seen even among individuals from the same family. The major clinical manifestations of ALGS are bile duct paucity on liver biopsy, cholestasis, congenital cardiac defects (primarily involving the pulmonary arteries), butterfly vertebrae, ophthalmologic abnormalities (most commonly posterior embryotoxon), and characteristic facial features. Renal abnormalities, growth failure, developmental delays, splenomegaly, and vascular abnormalities may also occur.

Long-chain hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency and trifunctional protein (TFP) deficiency are caused by impairment of mitochondrial TFP. TFP has three enzymatic activities – long-chain enoyl-CoA hydratase, long-chain 3-hydroxyacyl-CoA dehydrogenase, and long-chain 3-ketoacyl-CoA thiolase. In individuals with LCHAD deficiency, there is isolated deficiency of long-chain 3-hydroxyacyl-CoA dehydrogenase, while deficiency of all three enzymes occurs in individuals with TFP deficiency. Individuals with TFP deficiency can present with a severe-to-mild phenotype, while individuals with LCHAD deficiency typically present with a severe-to-intermediate phenotype. Neonates with the severe phenotype present within a few days of birth with hypoglycemia, hepatomegaly, encephalopathy, and often cardiomyopathy. The intermediate phenotype is characterized by hypoketotic hypoglycemia precipitated by infection or fasting in infancy. The mild (late-onset) phenotype is characterized by myopathy and/or neuropathy. Long-term complications include peripheral neuropathy and retinopathy.

In general, gallbladder disease (GBD) is one of the major digestive diseases. GBD prevalence is particularly high in some minority populations in the United States, including Native and Mexican Americans. Gallstones composed of cholesterol (cholelithiasis) are the common manifestations of GBD in western countries, including the United States. Most people with gallstones remain asymptomatic through their lifetimes; however, it is estimated that approximately 10 to 50% of individuals eventually develop symptoms. Significant risk factors associated with GBD are age, female sex, obesity (especially central obesity), lipids, diet, parity, type 2 diabetes (125853), medications, and Mexican American ethnicity. GBD appears to be strongly related to the metabolic syndrome (605552) and/or its major components, such as hyperinsulinism, dyslipidemia, and abdominal adiposity (Boland et al., 2002; Tsai et al., 2004). Infection, specifically by Helicobacter, has been implicated in cholelithiasis and cholecystitis (Silva et al., 2003; Maurer et al., 2005). Low phospholipid-associated cholelithiasis is a specific form of gallbladder disease characterized by young-adult onset of chronic cholestasis with intrahepatic sludge and cholesterol cholelithiasis. Affected individuals have recurrence of the disorder after cholecystectomy and show a favorable response to treatment with ursodeoxycholic acid (UDCA) (summary by Pasmant et al., 2012). Mutation in the ABCB4 gene can cause a spectrum of related diseases, including the more severe progressive familial intrahepatic cholestasis-3 (PFIC3; 602347), intrahepatic cholestasis of pregnancy-3 (ICP3; 614972), andoral contraceptive-induced cholestasis (OCIC; see 614972). Genetic Heterogeneity of Gallbladder Disease Two major susceptibility loci for symptomatic gallbladder disease have been identified on chromosome 1p in Mexican Americans (GBD2, 609918; GBD3, 609919). In addition, variations in the ABCG8 gene (605460) on chromosome 2p21 confer susceptibility to gallbladder disease (GBD4; 611465).

This autosomal recessive disorder is designated Meckel syndrome type 7 (MKS7) based on the classic phenotypic triad of (1) cystic renal disease; (2) a central nervous system abnormality, and (3) hepatic abnormalities, as defined by Meckel (1822), Salonen (1984), and Logan et al. (2011). According to these criteria, polydactyly is a variable feature. Herriot et al. (1991) and Al-Gazali et al. (1996) concluded that Dandy-Walker malformation can be the phenotypic manifestation of a central nervous system malformation in MKS. For a general phenotypic description and a discussion of genetic heterogeneity of Meckel syndrome, see MKS1 (249000).

Mitchell-Riley syndrome (MTCHRS) is characterized by neonatal diabetes, pancreatic hypoplasia, intestinal atresia, and gallbladder aplasia or hypoplasia. There is considerable phenotypic overlap between Mitchell-Riley syndrome and Martinez-Frias syndrome (601346), the latter being characterized by the features of the Mitchell-Riley syndrome except for neonatal diabetes, and including tracheoesophageal fistula in some patients (Smith et al., 2010).

CDGs, previously called carbohydrate-deficient glycoprotein syndromes, grew from hereditary multisystem disorders first recognized by Jaeken et al. (1980). The characteristic biochemical abnormality of CDGs is the hypoglycosylation of glycoproteins, which is routinely determined by isoelectric focusing of serum transferrin. Type I CDG comprises those disorders in which there is a defect in the assembly of lipid-linked oligosaccharides or their transfer onto nascent glycoproteins, whereas type II CDG comprises defects of trimming, elongation, and processing of protein-bound glycans. For a general discussion of CDGs, see CDG1A (212065). CDG1H is a severe form of CDG. The majority of patients have brain involvement, liver pathology, gastrointestinal symptoms, dysmorphism (including brachydactyly), eye involvement (especially cataract), and skin symptoms. Most patients die within the first year of life (summary by Marques-da-Silva et al., 2017).

Cranioectodermal dysplasia (CED) is a ciliopathy with skeletal involvement (narrow thorax, shortened proximal limbs, syndactyly, polydactyly, brachydactyly), ectodermal features (widely spaced hypoplastic teeth, hypodontia, sparse hair, skin laxity, abnormal nails), joint laxity, growth deficiency, and characteristic facial features (frontal bossing, low-set simple ears, high forehead, telecanthus, epicanthal folds, full cheeks, everted lower lip). Most affected children develop nephronophthisis that often leads to end-stage kidney disease in infancy or childhood, a major cause of morbidity and mortality. Hepatic fibrosis and retinal dystrophy are also observed. Dolichocephaly, often secondary to sagittal craniosynostosis, is a primary manifestation that distinguishes CED from most other ciliopathies. Brain malformations and developmental delay may also occur.

Hyperbiliverdinemia can manifest as green jaundice, which is a green discoloration of the skin, urine, serum, and other bodily fluids, due to increased biliverdin resulting from inefficient conversion to bilirubin. Although rarely reported, affected individuals appear to have symptoms only in the context of obstructive cholestasis and/or liver failure. In some cases, green jaundice can resolve after resolution of obstructive cholestasis. Green jaundice has also been associated with malnutrition, medication, and congenital biliary atresia (summary by Huffman et al., 2009).

Autosomal recessive mitochondrial complex III deficiency is a severe multisystem disorder with onset at birth of lactic acidosis, hypotonia, hypoglycemia, failure to thrive, encephalopathy, and delayed psychomotor development. Visceral involvement, including hepatopathy and renal tubulopathy, may also occur. Many patients die in early childhood, but some may show longer survival (de Lonlay et al., 2001; De Meirleir et al., 2003). Genetic Heterogeneity of Mitochondrial Complex III Deficiency Mitochondrial complex III deficiency can be caused by mutation in several different nuclear-encoded genes. See MC3DN2 (615157), caused by mutation in the TTC19 gene (613814) on chromosome 17p12; MC3DN3 (615158), caused by mutation in the UQCRB gene (191330) on chromosome 8q; MC3DN4 (615159), caused by mutation in the UQCRQ gene (612080) on chromosome 5q31; MC3DN5 (615160), caused by mutation in the UQCRC2 gene (191329) on chromosome 16p12; MC3DN6 (615453), caused by mutation in the CYC1 gene (123980) on chromosome 8q24; MC3DN7 (615824), caused by mutation in the UQCC2 gene (614461) on chromosome 6p21; MC3DN8 (615838), caused by mutation in the LYRM7 gene (615831) on chromosome 5q23; MC3DN9 (616111), caused by mutation in the UQCC3 gene (616097) on chromosome 11q12; and MC3DN10 (618775), caused by mutation in the UQCRFS1 gene (191327) on chromosome 19q12. See also MTYCB (516020) for a discussion of a milder phenotype associated with isolated mitochondrial complex III deficiency and mutations in a mitochondrial-encoded gene.

CDG2L is an autosomal recessive multisystem disorder apparent from birth or early infancy. It is characterized by poor growth, gastrointestinal and liver abnormalities, delayed psychomotor development, hypotonia, recurrent infections, hematologic abnormalities, increased bleeding tendency, and hyperhidrosis or hyperkeratosis. More variable features include nonspecific dysmorphic facial features and cardiac septal defects. The disorder often results in death in infancy or the first years of life (summary by Rymen et al., 2015). For a general discussion of CDGs, see CDG1A (212065) and CDG2A (212066).

The peroxisomal biogenesis disorder (PBD) Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 5 (CG5, equivalent to CG10 and CGF) have mutations in the PEX2 gene. For information on the history of PBD complementation groups, see 214100.

Any renal-hepatic-pancreatic dysplasia in which the cause of the disease is a mutation in the NPHP3 gene.

The nephronophthisis (NPH) phenotype is characterized by reduced renal concentrating ability, chronic tubulointerstitial nephritis, cystic renal disease, and progression to end-stage renal disease (ESRD) before age 30 years. Three age-based clinical subtypes are recognized: infantile, juvenile, and adolescent/adult. Infantile NPH can present in utero with oligohydramnios sequence (limb contractures, pulmonary hypoplasia, and facial dysmorphisms) or postnatally with renal manifestations that progress to ESRD before age 3 years. Juvenile NPH, the most prevalent subtype, typically presents with polydipsia and polyuria, growth retardation, chronic iron-resistant anemia, or other findings related to chronic kidney disease (CKD). Hypertension is typically absent due to salt wasting. ESRD develops at a median age of 13 years. Ultrasound findings are increased echogenicity, reduced corticomedullary differentiation, and renal cysts (in 50% of affected individuals). Histologic findings include tubulointerstitial fibrosis, thickened and disrupted tubular basement membrane, sporadic corticomedullary cysts, and normal or reduced kidney size. Adolescent/adult NPH is clinically similar to juvenile NPH, but ESRD develops at a median age of 19 years. Within a subtype, inter- and intrafamilial variability in rate of progression to ESRD is considerable. Approximately 80%-90% of individuals with the NPH phenotype have no extrarenal features (i.e., they have isolated NPH); ~10%-20% have extrarenal manifestations that constitute a recognizable syndrome (e.g., Joubert syndrome, Bardet-Biedl syndrome, Jeune syndrome and related skeletal disorders, Meckel-Gruber syndrome, Senior-Løken syndrome, Leber congenital amaurosis, COACH syndrome, and oculomotor apraxia, Cogan type).

RHPD2 is an autosomal recessive multisystemic disorder with severe abnormalities apparent in utero and often resulting in fetal death or death in infancy. The main organs affected include the kidney, liver, and pancreas, although other abnormalities, including cardiac, skeletal, and lung defects, may also be present. Affected individuals often have situs inversus. The disorder results from a defect in ciliogenesis and ciliary function, as well as in cell proliferation and epithelial morphogenesis; thus, the clinical manifestations are highly variable (summary by Grampa et al., 2016). For a discussion of genetic heterogeneity of renal-hepatic-pancreatic dysplasia, see RHPD1 (208540).

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500).

The nephronophthisis (NPH) phenotype is characterized by reduced renal concentrating ability, chronic tubulointerstitial nephritis, cystic renal disease, and progression to end-stage renal disease (ESRD) before age 30 years. Three age-based clinical subtypes are recognized: infantile, juvenile, and adolescent/adult. Infantile NPH can present in utero with oligohydramnios sequence (limb contractures, pulmonary hypoplasia, and facial dysmorphisms) or postnatally with renal manifestations that progress to ESRD before age 3 years. Juvenile NPH, the most prevalent subtype, typically presents with polydipsia and polyuria, growth retardation, chronic iron-resistant anemia, or other findings related to chronic kidney disease (CKD). Hypertension is typically absent due to salt wasting. ESRD develops at a median age of 13 years. Ultrasound findings are increased echogenicity, reduced corticomedullary differentiation, and renal cysts (in 50% of affected individuals). Histologic findings include tubulointerstitial fibrosis, thickened and disrupted tubular basement membrane, sporadic corticomedullary cysts, and normal or reduced kidney size. Adolescent/adult NPH is clinically similar to juvenile NPH, but ESRD develops at a median age of 19 years. Within a subtype, inter- and intrafamilial variability in rate of progression to ESRD is considerable. Approximately 80%-90% of individuals with the NPH phenotype have no extrarenal features (i.e., they have isolated NPH); ~10%-20% have extrarenal manifestations that constitute a recognizable syndrome (e.g., Joubert syndrome, Bardet-Biedl syndrome, Jeune syndrome and related skeletal disorders, Meckel-Gruber syndrome, Senior-Løken syndrome, Leber congenital amaurosis, COACH syndrome, and oculomotor apraxia, Cogan type).

Polyglucosan body myopathy-1 (PGBM1) is an autosomal recessive disorder characterized by onset in childhood of progressive proximal muscle weakness, resulting in difficulties in ambulation. Most patients also develop progressive dilated cardiomyopathy, which may necessitate cardiac transplant in severe cases. A small subset of patients present with severe immunodeficiency and a hyperinflammatory state in very early childhood (summary by Boisson et al., 2012 and Nilsson et al., 2013). Genetic Heterogeneity of Polyglucosan Body Myopathy See also PGBM2 (616199), caused by mutation in the GYG1 gene (603942) on chromosome 3q24.

The nephronophthisis (NPH) phenotype is characterized by reduced renal concentrating ability, chronic tubulointerstitial nephritis, cystic renal disease, and progression to end-stage renal disease (ESRD) before age 30 years. Three age-based clinical subtypes are recognized: infantile, juvenile, and adolescent/adult. Infantile NPH can present in utero with oligohydramnios sequence (limb contractures, pulmonary hypoplasia, and facial dysmorphisms) or postnatally with renal manifestations that progress to ESRD before age 3 years. Juvenile NPH, the most prevalent subtype, typically presents with polydipsia and polyuria, growth retardation, chronic iron-resistant anemia, or other findings related to chronic kidney disease (CKD). Hypertension is typically absent due to salt wasting. ESRD develops at a median age of 13 years. Ultrasound findings are increased echogenicity, reduced corticomedullary differentiation, and renal cysts (in 50% of affected individuals). Histologic findings include tubulointerstitial fibrosis, thickened and disrupted tubular basement membrane, sporadic corticomedullary cysts, and normal or reduced kidney size. Adolescent/adult NPH is clinically similar to juvenile NPH, but ESRD develops at a median age of 19 years. Within a subtype, inter- and intrafamilial variability in rate of progression to ESRD is considerable. Approximately 80%-90% of individuals with the NPH phenotype have no extrarenal features (i.e., they have isolated NPH); ~10%-20% have extrarenal manifestations that constitute a recognizable syndrome (e.g., Joubert syndrome, Bardet-Biedl syndrome, Jeune syndrome and related skeletal disorders, Meckel-Gruber syndrome, Senior-Løken syndrome, Leber congenital amaurosis, COACH syndrome, and oculomotor apraxia, Cogan type).

Senior-Loken syndrome-9 is an autosomal recessive disorder characterized by early-onset nephronophthisis and pigmentary retinopathy. Additional more variable features can include liver defects, skeletal anomalies, and obesity (summary by Bizet et al., 2015). For a phenotypic description and a discussion of genetic heterogeneity of Senior-Loken syndrome, see 266900.

Interstitial lung and liver disease is an autosomal recessive disorder characterized by onset of respiratory insufficiency and progressive liver disease in infancy or early childhood. Pathologic examination of lung lavage is consistent with pulmonary alveolar proteinosis (summary by Hadchouel et al., 2015).

Any mitochondrial DNA depletion syndrome in which the cause of the disease is a mutation in the TFAM gene.

Immunodeficiency-47 (IMD47) is an X-linked recessive complex syndrome characterized by liver dysfunction, recurrent bacterial infections, hypogammaglobulinemia, and defective glycosylation of serum proteins. Some patients also have neurologic abnormalities (summary by Jansen et al., 2016).

Neonatal sclerosing cholangitis (NSC) is a rare autosomal recessive form of severe liver disease with onset in infancy. Affected infants have jaundice, cholestasis, acholic stools, and progressive liver dysfunction resulting in fibrosis and cirrhosis; most require liver transplantation in the first few decades of life. Cholangiography shows patent biliary ducts, but there are bile duct irregularities (summary by Girard et al., 2016; Grammatikopoulos et al., 2016).

Trichohepatoenteric syndrome (THES), generally considered to be a neonatal enteropathy, is characterized by intractable diarrhea (seen in almost all affected children), woolly hair (seen in all), intrauterine growth restriction, facial dysmorphism, and short stature. Additional findings include poorly characterized immunodeficiency, recurrent infections, skin abnormalities, and liver disease. Mild intellectual disability (ID) is seen in about 50% of affected individuals. Less common findings include congenital heart defects and platelet anomalies. To date 52 affected individuals have been reported.

Combined oxidative phosphorylation deficiency-12 (COXPD12) is an autosomal recessive mitochondrial neurologic disorder characterized by onset in infancy of hypotonia and delayed psychomotor development, or early developmental regression, associated with T2-weighted hyperintensities in the deep cerebral white matter, brainstem, and cerebellar white matter. Serum lactate is increased due to a defect in mitochondrial respiration. There are 2 main phenotypic groups: those with a milder disease course and some recovery of skills after age 2 years, and those with a severe disease course resulting in marked disability (summary by Steenweg et al., 2012). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Hypermethioninemia due to adenosine kinase deficiency is an autosomal recessive inborn error of metabolism characterized by global developmental delay, early-onset seizures, mild dysmorphic features, and characteristic biochemical anomalies, including persistent hypermethioninemia with increased levels of S-adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy); homocysteine is typically normal (summary by Bjursell et al., 2011).

Infantile liver failure syndrome-3 is an autosomal recessive disorder characterized by recurrent episodes of acute liver failure during intercurrent febrile illness. Patients first present in infancy or early childhood, and there usually is complete recovery between episodes with conservative treatment. Affected individuals also have skeletal anomalies of the vertebral bodies and femoral heads (summary by Cousin et al., 2019). For a discussion of genetic heterogeneity of infantile liver failure syndrome, see ILFS1 (615438).

Rajab interstitial lung disease with brain calcifications-1 (RILDBC1) is an autosomal recessive multisystem disorder with a highly variable phenotype. Most patients present in infancy or early childhood with poor growth and interstitial lung disease, which may lead to death. Some may also have liver, skeletal, and renal abnormalities, and most have intracranial calcifications on brain imaging. Some may have early impaired motor development, but most have normal cognitive development (summary by Xu et al., 2018). Genetic Heterogeneity of Rajab Interstitial Lung Disease with Brain Calcifications Also see Rajab interstitial disease with brain calcifications-2 (RILDBC2; 619013), caused by mutation in the FARSA gene (602918).

Osteootohepatoenteric syndrome (OOHE) is characterized by a variable combination of bone fragility, hearing loss, cholestasis, and congenital diarrhea. Some patients also display mild developmental delay and intellectual disability (Esteve et al., 2018).

DEGCAGS syndrome is an autosomal recessive syndromic neurodevelopmental disorder characterized by global developmental delay, coarse and dysmorphic facial features, and poor growth and feeding apparent from infancy. Affected individuals have variable systemic manifestations often with significant structural defects of the cardiovascular, genitourinary, gastrointestinal, and/or skeletal systems. Additional features may include sensorineural hearing loss, hypotonia, anemia or pancytopenia, and immunodeficiency with recurrent infections. Death in childhood may occur (summary by Bertoli-Avella et al., 2021).

Neurodevelopmental disorder with hypotonia and dysmorphic facies (NEDHYDF) is characterized by global developmental delay and hypotonia apparent from birth. Affected individuals have variably impaired intellectual development, often with speech delay and delayed walking. Seizures are generally not observed, although some patients may have single seizures or late-onset epilepsy. Most patients have prominent dysmorphic facial features. Additional features may include congenital cardiac defects (without arrhythmia), nonspecific renal anomalies, joint contractures or joint hyperextensibility, dry skin, and cryptorchidism. There is significant phenotypic variability in both the neurologic and extraneurologic manifestations (summary by Tan et al., 2022).

Biliary, renal, neurologic, and skeletal syndrome (BRENS) is an autosomal recessive complex ciliopathy with multisystemic manifestations. The most common presentation is severe neonatal cholestasis that progresses to liver fibrosis and cirrhosis. Most patients have additional clinical features suggestive of a ciliopathy, including postaxial polydactyly, hydrocephalus, retinal abnormalities, and situs inversus. Additional features of the syndrome may include congenital cardiac defects, echogenic kidneys with renal failure, ocular abnormalities, joint hyperextensibility, and dysmorphic facial features. Some patients have global developmental delay. Brain imaging typically shows dilated ventricles, hypomyelination, and white matter abnormalities, although some patients have been described with abnormal pituitary development (summary by Shaheen et al., 2020 and David et al., 2020).

Progressive intrahepatic cholestasis-7 with or without hearing loss (PFIC7) is an autosomal recessive liver disorder characterized by infantile-onset jaundice and itching associated with cholestasis, elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and normal gamma glutamyltransferase (GGT). Liver biopsy shows hepatocellular and canalicular cholestasis with fibrotic changes. Many patients have resolution of the liver abnormalities with age, although some may have persistent liver enzyme abnormalities or splenomegaly. A subset of patients develops hearing loss in childhood between early infancy and the teenage years. Rifampicin may be effective for pruritis (summary by Maddirevula et al., 2019). For a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Progressive familial intrahepatic cholestasis-8 (PFIC8) is an autosomal recessive disorder characterized by cholestasis and high gamma-glutamyltransferase presenting in the infantile period (summary by Unlusoy Aksu et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of PFIC, see PFIC1 (211600).

Immunodeficiency-87 and autoimmunity (IMD87) is an autosomal recessive immunologic disorder with wide phenotypic variation and severity. Affected individuals usually present in infancy or early childhood with increased susceptibility to infections, often Epstein-Barr virus (EBV), as well as with lymphadenopathy or autoimmune manifestations, predominantly hemolytic anemia. Laboratory studies may show low or normal lymphocyte numbers, often with skewed T-cell subset ratios. The disorder results primarily from defects in T-cell function, which causes both immunodeficiency and overall immune dysregulation (summary by Serwas et al., 2019 and Fournier et al., 2021).

Recurrent respiratory infections and failure to thrive with or without diarrhea (RIFTD) is characterized by neonatal onset of chronic cough, episodic wheezing, recurrent lower respiratory tract infections, chronic diarrhea, and failure to thrive. Despite the resemblance to cystic fibrosis (CF; 219700), these patients have normal sweat chloride and pancreatic elastase tests (Bertoli-Avella et al., 2022).

Progressive familial intrahepatic cholestasis-12 (PFIC12) is characterized by neonatal-onset jaundice and conjugated hyperbilirubinemia, associated with intense pruritus. Transaminases are mildly elevated but GGT (see 612346) is normal. Hepatosplenomegaly and mildly prolonged activated partial thromboplastin time (APTT) have been observed in some patients (Qiu et al., 2019).

Systemic autoinflammatory disease with vasculitis (SAIDV) is an autosomal dominant disorder that manifests soon after birth with features such as purpuric skin rash, fever, hepatosplenomegaly, and elevated C-reactive protein (CRP; 123260). Laboratory studies may show leukocytosis, thrombocytopenia, and autoantibodies. A subset of patients develop progressive liver involvement that may result in fibrosis. Other systemic features, such as periorbital edema, conjunctivitis, infections, abdominal pain, and arthralgia are usually observed. Mutations occur de novo. De Jesus et al. (2023) referred to this disorder as LAVLI (LYN kinase-associated vasculopathy and liver fibrosis).

Congenital disorder of glycosylation type IIaa (CDG2AA) is an autosomal recessive disorder characterized by infantile mortality due to liver disease, skeletal abnormalities, and protein glycosylation defects (Linders et al., 2021). For an overview of congenital disorders of glycosylation, see CDG1A (212065) and CDG2A (212066).