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Hypotrichosis simplex (HS) or hereditary hypotrichosis simplex (HHS) is characterized by reduced pilosity over the scalp and body (with sparse, thin, and short hair) in the absence of other anomalies.
ORPHA:55654Classification level: Disorder
Prevalence is unknown but numerous large pedigrees with several affected members have been described. Both men and women are equally affected.
Hair loss is diffuse and progressive and usually begins during early childhood. Body hair may also be sparse with variable involvement of the eyebrows, eyelashes, and pubic and axillary hair. There are no anomalies of the skin, nails or teeth. A scalp-limited form, hypotrichosis simplex of the scalp (see this term) has also been reported with mutations in the corneodesmosin (CDSN) gene.
Both autosomal dominant and recessive modes of transmission have been reported for HHS.Autosomal dominant HHS affecting both scalp and body hair has been reported in one Italian and two Pakistani families as due to mutations in the APCDD1 gene mapped to 18p11.22. Three clinically similar forms of localized autosomal recessive hypotrichosis (LAH1, LAH2 and LAH3) have been identified within the last years. The locus for LAH1 (involving mainly the hair of the scalp, chest, arms and legs) has been mapped to 18q12.1 and mutations in the desmoglein-4 (DSG4) gene have been identified. The locus for LAH2 (characterized by sparse or absent scalp, axillary and body hair, and sparse eyebrows and eyelashes) has been mapped to 3q27.3 and mutations in the lipase-H (LIPH) gene have been identified. The locus for LAH3 (characterized by progressive loss of scalp hair, sparse body hair, and normal eyebrows, eyelashes, and pubic and axillary hair) has been mapped to 13q14.11-q21.32 and mutations have been identified in a G protein-coupled receptor gene (P2RY5). These receptors belong to the group of lipophosphatidic acid (LPA) receptors and are therefore designated as LPAR6.
Management and treatment
There is no treatment for hypotrichosis simplex available to date.