Apert syndrome is characterized by the presence of multisuture craniosynostosis, midface retrusion, and syndactyly of the hands with fusion of the second through fourth nails. Almost all affected individuals have coronal craniosynostosis, and a majority also have involvement of the sagittal and lambdoid sutures. The midface in Apert syndrome is underdeveloped as well as retruded; a subset of affected individuals have cleft palate. The hand in Apert syndrome always includes fusion of the middle three digits; the thumb and fifth finger are sometimes also involved. Feeding issues, dental abnormalities, hearing loss, hyperhidrosis, and progressive synostosis of multiple bones (skull, hands, feet, carpus, tarsus, and cervical vertebrae) are also common. Multilevel airway obstruction may be present and can be due to narrowing of the nasal passages, tongue-based airway obstruction, and/or tracheal anomalies. Nonprogressive ventriculomegaly is present in a majority of individuals, with a small subset having true hydrocephalus. Most individuals with Apert syndrome have normal intelligence or mild intellectual disability; moderate-to-severe intellectual disability has been reported in some individuals. A minority of affected individuals have structural cardiac abnormalities, true gastrointestinal malformations, and anomalies of the genitourinary tract.

Crouzon syndrome is an autosomal dominant disorder characterized by craniosynostosis causing secondary alterations of the facial bones and facial structure. Common features include hypertelorism, exophthalmos and external strabismus, parrot-beaked nose, short upper lip, hypoplastic maxilla, and a relative mandibular prognathism (Reardon et al., 1994; Glaser et al., 2000).

Classic Saethre-Chotzen syndrome (SCS) is characterized by coronal synostosis (unilateral or bilateral), facial asymmetry (particularly in individuals with unicoronal synostosis), strabismus, ptosis, and characteristic appearance of the ear (small pinna with a prominent superior and/or inferior crus). Syndactyly of digits two and three of the hand is variably present. Cognitive development is usually normal, although those with a large genomic deletion are at an increased risk for intellectual challenges. Less common manifestations of SCS include other skeletal findings (parietal foramina, vertebral segmentation defects, radioulnar synostosis, maxillary hypoplasia, ocular hypertelorism, hallux valgus, duplicated or curved distal hallux), hypertelorism, palatal anomalies, obstructive sleep apnea, increased intracranial pressure, short stature, and congenital heart malformations.

Pfeiffer syndrome is an autosomal dominant craniosynostosis syndrome with characteristic anomalies of the hands and feet. Three clinical subtypes, which have important diagnostic and prognostic implications, have been identified. Type 1, the classic syndrome, is compatible with life and consists of craniosynostosis, midface deficiency, broad thumbs, broad great toes, brachydactyly, and variable syndactyly. Type 2 consists of cloverleaf skull with Pfeiffer hands and feet, together with ankylosis of the elbows. Type 3 is similar to type 2 but without cloverleaf skull. Ocular proptosis is severe, and the anterior cranial base is markedly short. Various visceral malformations have been found in association with type 3. Early demise is characteristic of types 2 and 3 (Cohen, 1993). Cohen and Barone (1994) further tabulated the findings in the 3 types of Pfeiffer syndrome.

Craniofrontonasal syndrome is an X-linked developmental disorder that shows paradoxically greater severity in heterozygous females than in hemizygous males. Females have frontonasal dysplasia, craniofacial asymmetry, craniosynostosis, bifid nasal tip, grooved nails, wiry hair, and abnormalities of the thoracic skeleton, whereas males typically show only hypertelorism (Twigg et al., 2004; Wieland et al., 2004).

Treacher Collins syndrome (TCS) is characterized by bilateral and symmetric downslanting palpebral fissures, malar hypoplasia, micrognathia, and external ear abnormalities. Hypoplasia of the zygomatic bones and mandible can cause significant feeding and respiratory difficulties. About 40%-50% of individuals have conductive hearing loss attributed most commonly to malformation of the ossicles and hypoplasia of the middle ear cavities. Inner ear structures tend to be normal. Other, less common abnormalities include cleft palate and unilateral or bilateral choanal stenosis or atresia. Typically intellect is normal.

Baller-Gerold syndrome (BGS) can be suspected at birth in an infant with craniosynostosis and upper limb abnormality. The coronal suture is most commonly affected; the metopic, lambdoid, and sagittal sutures may also be involved alone or in combination. Upper limb abnormality can include a combination of thumb hypo- or aplasia and radial hypo- or aplasia and may be asymmetric. Malformation or absence of carpal or metacarpal bones has also been described. Skin lesions may appear anytime within the first few years after birth, typically beginning with erythema of the face and extremities and evolving into poikiloderma. Slow growth is apparent in infancy with eventual height and length typically at 4 SD below the mean.

Jackson-Weiss syndrome (JWS) is an autosomal dominant condition consisting of craniosynostosis characterized by premature fusion of the cranial sutures as well as radiographic anomalies of the feet (summary by Heike et al., 2001).

The term '3MC syndrome' encompasses 4 rare autosomal recessive disorders that were previously designated the Carnevale, Mingarelli, Malpuech, and Michels syndromes, respectively. The main features of these syndromes are facial dysmorphism that includes hypertelorism, blepharophimosis, blepharoptosis, and highly arched eyebrows, which are present in 70 to 95% of cases. Cleft lip and palate, postnatal growth deficiency, cognitive impairment, and hearing loss are also consistent findings, occurring in 40 to 68% of cases. Craniosynostosis, radioulnar synostosis, and genital and vesicorenal anomalies occur in 20 to 30% of cases. Rare features include anterior chamber defects, cardiac anomalies, caudal appendage, umbilical hernia (omphalocele), and diastasis recti (summary by Rooryck et al., 2011). Genetic Heterogeneity of 3MC Syndrome Also see 3MC syndrome-2 (3MC2; 265050), caused by mutation in the COLEC11 gene (612502), and 3MC syndrome-3 (3MC3; 248340), caused by mutation in the COLEC1 gene (607620).

Holoprosencephaly-craniosynostosis syndrome is a rare developmental defect during embryogenesis syndrome characterized by the association of primary craniosynostosis (usually involving the coronal and metopic sutures) with holoprosencephaly (ranging from alobar to, most commonly, semilobar) and various skeletal anomalies (typically, hand and feet anomalies including fifth digit clinodactyly, hypoplastic phalanges and cone-shaped epiphyses, small vertebral bodies, scoliosis, coxa valga and/or flexion deformities of hips). Craniofacial asymmetry, microcephaly, brachy/plagiocephaly, short stature and psychomotor delay are additional common features.

Craniosynostosis (CRS) is a primary abnormality of skull growth involving premature fusion of the cranial sutures such that the growth velocity of the skull often cannot match that of the developing brain. This produces skull deformity and, in some cases, raises intracranial pressure, which must be treated promptly to avoid permanent neurodevelopmental disability (summary by Fitzpatrick, 2013). Craniosynostosis-4 (CRS4) includes lambdoid, sagittal, metopic, coronal, and multisuture forms. For a discussion of genetic heterogeneity of craniosynostosis, see CRS1 (123100).

Syndrome with the association of skeletal abnormalities, cutis laxa, craniostenosis, ambiguous genitalia, psychomotor retardation and facial abnormalities. So far, it has been described in two males (maternal first cousins). The mode of inheritance was suggested to be X-linked recessive.

Hypomandibular faciocranial syndrome consists of craniosynostosis, prominent eyes, deficient midface and zygomatic arches, short nose with anteverted nares, protruding lower face, minute oral aperture, persistent buccopharyngeal membrane, severe mandibular hypoplasia, and various extracephalic anomalies (summary by Gorlin et al., 2001).

CDAGS syndrome is characterized by craniosynostosis and clavicular hypoplasia, delayed closure of the fontanel, anal and genitourinary anomalies, and skin eruption of porokeratotic lesions (Mendoza-Londono et al., 2005).

Muenke syndrome is defined by the presence of the specific FGFR3 pathogenic variant – c.749C>G – that results in the protein change p.Pro250Arg. Muenke syndrome is characterized by considerable phenotypic variability: features may include coronal synostosis (more often bilateral than unilateral); synostosis of other sutures, all sutures (pan synostosis), or no sutures; or macrocephaly. Bilateral coronal synostosis typically results in brachycephaly (reduced anteroposterior dimension of the skull), although turribrachycephaly (a "tower-shaped" skull) or a cloverleaf skull can be observed. Unilateral coronal synostosis results in anterior plagiocephaly (asymmetry of the skull and face). Other craniofacial findings typically include: temporal bossing; widely spaced eyes, ptosis or proptosis (usually mild); midface retrusion (usually mild); and highly arched palate or cleft lip and palate. Strabismus is common. Other findings can include: hearing loss (in 33%-100% of affected individuals); developmental delay (~33%); epilepsy; intracranial anomalies; intellectual disability; carpal bone and/or tarsal bone fusions; brachydactyly, broad toes, broad thumbs, and/or clinodactyly; and radiographic findings of thimble-like (short and broad) middle phalanges and/or cone-shaped epiphyses. Phenotypic variability is considerable even within the same family. Of note, some individuals who have the p.Pro250Arg pathogenic variant may have no signs of Muenke syndrome on physical or radiographic examination.

SLC25A24 Fontaine progeroid syndrome is a multisystem connective tissue disorder characterized by poor growth, abnormal skeletal features, and distinctive craniofacial features with sagging, thin skin, and decreased subcutaneous fat suggesting an aged appearance that is most pronounced in infancy and improves with time. Characteristic radiographic features include turribrachycephaly with widely open anterior fontanelle, craniosynostosis, and anomalies of the terminal phalanges. Cardiovascular, genitourinary, ocular, and gastrointestinal abnormalities may also occur. To date, 13 individuals with a molecularly confirmed diagnosis of SLC25A24 Fontaine progeroid syndrome have been described.

Cytochrome P450 oxidoreductase deficiency (PORD) is a disorder of steroidogenesis with a broad phenotypic spectrum including cortisol deficiency, altered sex steroid synthesis, disorders of sex development (DSD), and skeletal malformations of the Antley-Bixler syndrome (ABS) phenotype. Cortisol deficiency is usually partial, with some baseline cortisol production but failure to mount an adequate cortisol response in stress. Mild mineralocorticoid excess can be present and causes arterial hypertension, usually presenting in young adulthood. Manifestations of altered sex steroid synthesis include ambiguous genitalia/DSD in both males and females, large ovarian cysts in females, poor masculinization and delayed puberty in males, and maternal virilization during pregnancy with an affected fetus. Skeletal malformations can manifest as craniosynostosis, mid-face retrusion with proptosis and choanal stenosis or atresia, low-set dysplastic ears with stenotic external auditory canals, hydrocephalus, radiohumeral synostosis, neonatal fractures, congenital bowing of the long bones, joint contractures, arachnodactyly, and clubfeet; other anomalies observed include urinary tract anomalies (renal pelvic dilatation, vesicoureteral reflux). Cognitive impairment is of minor concern and likely associated with the severity of malformations; studies of developmental outcomes are lacking.

The GPAPP-type of chondrodysplasia with joint dislocations is an autosomal recessive disorder characterized by short stature, chondrodysplasia with brachydactyly, congenital joint dislocations, cleft palate, and facial dysmorphism (Vissers et al., 2011).

CRSDA is an autosomal recessive disorder characterized by craniosynostosis, maxillary hypoplasia, and dental anomalies, including malocclusion, delayed and ectopic tooth eruption, and/or supernumerary teeth. Some patients also display minor digit anomalies, such as syndactyly and/or clinodactyly (summary by Nieminen et al., 2011).

Bent bone dysplasia syndrome-1 (BBDS1) is a perinatal lethal skeletal dysplasia characterized by poor mineralization of the calvarium, craniosynostosis, dysmorphic facial features, prenatal teeth, hypoplastic pubis and clavicles, osteopenia, and bent long bones (Merrill et al., 2012). Genetic Heterogeneity of Bent Bone Dysplasia Syndrome BBDS2 (620076) is caused by mutation in the LAMA5 gene (601033) on chromosome 20q13.

Hennekam lymphangiectasia-lymphedema syndrome (HKLLS1) is an autosomal recessive disorder characterized by generalized lymphatic dysplasia affecting various organs, including the intestinal tract, pericardium, and limbs. Additional features of the disorder include facial dysmorphism and cognitive impairment (summary by Alders et al., 2014). Genetic Heterogeneity of Hennekam Lymphangiectasia-Lymphedema Syndrome See also HKLLS2 (616006), caused by mutation in the FAT4 gene (612411) on chromosome 4q28, and HKLLS3 (618154), caused by mutation in the ADAMTS3 gene (605011) on chromosome 4q13.

Cole-Carpenter syndrome-2 (CLCRP2) is a skeletal dysplasia associated with low bone mass or an osteogenesis imperfecta-like syndrome. It is characterized by bone fragility with craniosynostosis, ocular proptosis, hydrocephalus, and distinctive facial features such as marked frontal bossing, midface hypoplasia, and micrognathia (summary by Takeyari et al., 2018).

About half of all people with trichothiodystrophy have a photosensitive form of the disorder, which causes them to be extremely sensitive to ultraviolet (UV) rays from sunlight. They develop a severe sunburn after spending just a few minutes in the sun. However, for reasons that are unclear, they do not develop other sun-related problems such as excessive freckling of the skin or an increased risk of skin cancer. Many people with trichothiodystrophy report that they do not sweat.\n\nTrichothiodystrophy is also associated with recurrent infections, particularly respiratory infections, which can be life-threatening. People with trichothiodystrophy may have abnormal red blood cells, including red blood cells that are smaller than normal. They may also have elevated levels of a type of hemoglobin called A2, which is a protein found in red blood cells. Other features of trichothiodystrophy can include dry, scaly skin (ichthyosis); abnormalities of the fingernails and toenails; clouding of the lens in both eyes from birth (congenital cataracts); poor coordination; and skeletal abnormalities including degeneration of both hips at an early age.\n\nIntellectual disability and delayed development are common in people with trichothiodystrophy, although most affected individuals are highly social with an outgoing and engaging personality. Some people with trichothiodystrophy have brain abnormalities that can be seen with imaging tests. A common neurological feature of this disorder is impaired myelin production (dysmyelination). Myelin is a fatty substance that insulates nerve cells and promotes the rapid transmission of nerve impulses.\n\nMothers of children with trichothiodystrophy may experience problems during pregnancy including pregnancy-induced high blood pressure (preeclampsia) and a related condition called HELLP syndrome that can damage the liver. Babies with trichothiodystrophy are at increased risk of premature birth, low birth weight, and slow growth. Most children with trichothiodystrophy have short stature compared to others their age. \n\nThe signs and symptoms of trichothiodystrophy vary widely. Mild cases may involve only the hair. More severe cases also cause delayed development, significant intellectual disability, and recurrent infections; severely affected individuals may survive only into infancy or early childhood.\n\nIn people with trichothiodystrophy, tests show that the hair is lacking sulfur-containing proteins that normally gives hair its strength. A cross section of a cut hair shows alternating light and dark banding that has been described as a "tiger tail."\n\nTrichothiodystrophy, commonly called TTD, is a rare inherited condition that affects many parts of the body. The hallmark of this condition is hair that is sparse and easily broken. 

Cole-Carpenter syndrome is characterized by bone fragility, craniosynostosis, ocular proptosis, hydrocephalus, and distinctive facial features (Cole and Carpenter, 1987). Genetic Heterogeneity of Cole-Carpenter Syndrome Cole-Carpenter syndrome-2 (CLCRP2; 616294) is caused by mutation in the SEC24D gene (607186).

Carpenter syndrome is a rare autosomal recessive disorder with the cardinal features of acrocephaly with variable synostosis of the sagittal, lambdoid, and coronal sutures; peculiar facies; brachydactyly of the hands with syndactyly; preaxial polydactyly and syndactyly of the feet; congenital heart defects; growth retardation; mental retardation; hypogenitalism; and obesity. In addition, cerebral malformations, oral and dental abnormalities, coxa valga, genu valgum, hydronephrosis, precocious puberty, and hearing loss may be observed (summary by Altunhan et al., 2011). Genetic Heterogeneity of Carpenter Syndrome Carpenter syndrome-2 (CRPT2; 614976), in which the features of Carpenter syndrome are sometimes associated with defective lateralization, is caused by mutation in the MEGF8 gene (604267).

Teebi hypertelorism syndrome-1 (TBHS1) is an autosomal dominant disorder characterized by hypertelorism with upslanting palpebral fissures, prominent forehead, broad and depressed nasal bridge with short nose, thick eyebrows, and widow's peak. Additional features include small broad hands with mild interdigital webbing and shawl scrotum. Umbilical malformations, cardiac defects, natal teeth, cleft lip/palate, congenital diaphragmatic hernia, and malformations of the central nervous system (ventriculomegaly, abnormal corpus callosum) have also been reported. Development is typically normal, although some patients with developmental delays have been reported (summary by Bhoj et al., 2015). Genetic Heterogeneity of Teebi Hypertelorism Syndrome Teebi hypertelorism syndrome-2 (TBHS2; 619736) is caused by mutation in the CDH11 gene (600023) on chromosome 16q21.