Trichothiodystrophy is a rare autosomal recessive disorder in which patients have brittle, sulfur-deficient hair that displays a diagnostic alternating light and dark banding pattern, called 'tiger tail banding,' under polarizing microscopy. TTD patients display a wide variety of clinical features, including cutaneous, neurologic, and growth abnormalities. Common additional clinical features are ichthyosis, intellectual/developmental disabilities, decreased fertility, abnormal characteristics at birth, ocular abnormalities, short stature, and infections. There are both photosensitive and nonphotosensitive forms of the disorder (summary by Faghri et al., 2008). Sabinas brittle hair syndrome (211390) is another form of nonphotosensitive TTD. For a discussion of genetic heterogeneity of trichothiodystrophy, see 601675.

Berardinelli-Seip congenital lipodystrophy (BSCL) is usually diagnosed at birth or soon thereafter. Because of the absence of functional adipocytes, lipid is stored in other tissues, including muscle and liver. Affected individuals develop insulin resistance and approximately 25%-35% develop diabetes mellitus between ages 15 and 20 years. Hepatomegaly secondary to hepatic steatosis and skeletal muscle hypertrophy occur in all affected individuals. Hypertrophic cardiomyopathy is reported in 20%-25% of affected individuals and is a significant cause of morbidity from cardiac failure and early mortality.

Chromosomal mosaicism as described here refers to a tendency to chromosomal nondisjunction. See also premature chromatid separation (PCS; 176430), which may also predispose to chromosomal nondisjunction.

Spinal and bulbar muscular atrophy (SBMA) is a gradually progressive neuromuscular disorder in which degeneration of lower motor neurons results in muscle weakness, muscle atrophy, and fasciculations. SBMA occurs only in males. Affected individuals often show gynecomastia, testicular atrophy, and reduced fertility as a result of mild androgen insensitivity.

CILD20 is an autosomal recessive ciliopathy characterized by infantile onset of chronic sinopulmonary infections resulting from immotile cilia and defective clearance. Patients may also have situs inversus or cardiac anomalies. Electron microscopy of respiratory epithelial cells shows absence of the outer dynein arms. Unlike other forms of CILD, patients with CILD20 do not appear to be infertile. For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.