Hypotrichosis simplex refers to a group of hereditary isolated alopecias characterized by diffuse and progressive hair loss, usually beginning in early childhood (Pasternack et al., 2008). Localized autosomal recessive hypotrichosis (LAH) is characterized by fragile hairs that break easily, leaving short, sparse scalp hairs. The disorder affects the trunk and extremities as well as the scalp, and the eyebrows and eyelashes may also be involved, whereas beard, pubic, and axillary hairs are largely spared. In addition, patients can develop hyperkeratotic follicular papules, erythema, and pruritus in affected areas (summary by Schaffer et al., 2006).
Woolly hair (WH) refers to a group of hair shaft disorders that are characterized by fine and tightly curled hair. Compared to normal curly hair that is observed in some populations, WH grows slowly and stops growing after a few inches. Under light microscopy, WH shows some structural anomalies, including trichorrhexis nodosa and tapered ends (summary by Petukhova et al., 2009). Several families have been reported in which some affected individuals exhibit features of hypotrichosis and others have woolly scalp hair (Khan et al., 2011).
Woolly hair is also a feature of several syndromes, such as Naxos disease (601214) and cardiofaciocutaneous syndrome (115150) (Petukhova et al., 2009), or the palmoplantar keratoderma and cardiomyopathy syndrome (601214) (Carvajal-Huerta, 1998).
Genetic Heterogeneity of Hypotrichosis and Woolly Hair
For a discussion of genetic heterogeneity of nonsyndromic hypotrichosis, see HYPT1 (605389).
For a discussion of genetic heterogeneity of localized hypotrichosis, see LAH1 (HYPT6; 607903).
Another form of autosomal recessive woolly hair with or without hypotrichosis (ARWH2; 604379) is caused by mutation in the LIPH gene (607365) and is allelic to autosomal recessive localized hypotrichosis (LAH2). ARWH3 (616760) is caused by mutation in the KRT25 gene (616646) on chromosome 17q21.
An autosomal dominant form of woolly hair with hypotrichosis (HYPT13; 615896) is caused by mutation in the KRT71 gene (608245) on chromosome 12q13. Another autosomal dominant form of woolly hair (ADWH; 194300) with normal hair density is caused by mutation in the KRT74 gene (608248) on chromosome 12q13, and is allelic to an autosomal dominant form of hypotrichosis simplex of the scalp (HYPT3; 613981) as well as an ectodermal dysplasia of the hair/nail type (ECTD7; 614929). [from
OMIM]