Hypotrichosis is an abnormal condition characterized by decreased hair density and various defects in hair
structure and growth patterns. In particular, in woolly hair, hypotrichosis is characterized by a tightly curled
structure and abnormal growth. In this study, we present a detailed comparative examination of individuals
affected by autosomal-recessive hypotrichosis (ARH), which distinguishes two types of ARH. Earlier, we
demonstrated that exon 4 deletion in the lipase H gene caused an ARH (hypotrichosis 7; MIM: 604379) in
populations of the Volga-Ural region of Russia. Screening for this mutation in all affected individuals revealed
its presence only in the group with the hypotrichosis 7 phenotype. Other patients formed a separate group of
woolly hair-associated ARH, with a homozygous missense mutation c.712G>T (p.Val238Leu) in a highly
conserved position of type I keratin KRT25 (K25). Haplotype analysis indicated a founder effect. An expression
study in the HaCaT cell line demonstrated a deleterious effect of the p.Val238Leu mutation on the formation of
keratin intermediate filaments. Hence, we have identified a previously unreported missense mutation in the
KRT25 gene causing ARH with woolly hair.