Primary lymphedema is caused by anatomic or functional defects in the lymphatic system, resulting in chronic swelling of body parts. There may be accompanying nail and skin changes, such as nail dysplasia or papillomatosis. Onset is usually at birth or in early childhood but can occur later, and the severity is variable (summary by Gordon et al., 2013 and Balboa-Beltran et al., 2014). Genetic Heterogeneity of Lymphatic Malformation Primary lymphedema is genetically heterogeneous: see also LMPHM2 (611944), which maps to chromosome 6q16.2-q22.1; LMPHM3 (613480), caused by mutation in the GJC2 gene (608803) on chromosome 1q42; LMPHM4 (615907), caused by mutation in the VEGFC gene (601528) on chromosome 4q34; LMPHM5 (153200); LMPHM6 (616843), caused by mutation in the PIEZO1 gene (611184) on chromosome 16q24; LMPHM7 (617300), caused by mutation in the EPHB4 gene (600011) on chromosome 7q22; LMPHM8 (618773), caused by mutation in the CALCRL gene (114190) on chromosome 2q31; LMPHM9 (619319), caused by mutation in the CELSR1 gene (604523) on chromosome 22q13; LMPHM10 (610369), caused by mutation in the ANGPT2 gene (601922) on chromosome 8p23; LMPHM11 (619401), caused by mutation in the TIE1 gene (600222) on chromosome 1p34; LMPHM12 (620014), caused by mutation in the MDFIC gene (614511) on chromosome 7q31; LMPHM13 (620244), caused by mutation in the THSD1 gene (616821) on chromosome 13q14; and LMPHM14 (620602), caused by mutation in the ERG gene (165080) on chromosome 21q22. Lymphedema can also be a feature of syndromic disorders such as lymphedema-distichiasis syndrome (153400), which is caused by mutation in the FOXC2 gene (602402), and various forms of nonimmune hydrops fetalis (NIHF; see 236750).

X-linked reticulate pigmentary disorder shows more severe manifestations in hemizygous males compared to heterozygous females. Affected males have early onset of recurrent respiratory infections and failure to thrive resulting from inflammatory gastroenteritis or colitis. Patients also show reticular pigmentation abnormalities of the skin and may develop corneal scarring. Carrier females may be unaffected or have only pigmentary abnormalities along the lines of Blaschko (summary by Starokadomskyy et al., 2016).

Epidermolysis bullosa simplex (EBS) is characterized by fragility of the skin (and mucosal epithelia in some instances) that results in non-scarring blisters and erosions caused by minor mechanical trauma. EBS is distinguished from other types of epidermolysis bullosa (EB) or non-EB skin fragility syndromes by the location of the blistering in relation to the dermal-epidermal junction. In EBS, blistering occurs within basal keratinocytes. The severity of blistering ranges from limited to hands and feet to widespread involvement. Additional features can include hyperkeratosis of the palms and soles (keratoderma), nail dystrophy, milia, and hyper- and/or hypopigmentation. Rare EBS subtypes have been associated with additional clinical features including pyloric atresia, muscular dystrophy, cardiomyopathy, and/or nephropathy.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Any Meier-Gorlin syndrome in which the cause of the disease is a mutation in the CDC45 gene.

Neurodevelopmental-craniofacial syndrome with variable renal and cardiac abnormalities (NECRC) is an autosomal dominant disorder characterized by dysmorphic craniofacial features associated with mild developmental delay, mildly impaired intellectual development or learning difficulties, speech delay, and behavioral abnormalities. About half of patients have congenital anomalies of the kidney and urinary tract (CAKUT) and/or congenital cardiac defects, including septal defects (Connaughton et al., 2020).