[Alopecia and hypotrichosis in childhood: clinical features and diagnosis].

The monogenic inherited isolated alopecias comprise a group of clinically and genetically heterogeneous disorders with decreased or absent hair. Clinical classification of the isolated alopecias is based upon the onset of the disorder, the regions affected, and the structure of the hair shaft. Men and women are equally affected, and the mode of inheritance is autosomal dominant or autosomal recessive. Therapy does not exist for these rare forms of alopecia. However, molecular genetic diagnosis is possible for the identification of the genetic causes and for the specification of the recurrence risk. Since the identification of the keratin gene KRT86 as a cause of the so called monilethrix in 1997, mutations in eleven other genes have been identified for various isolated alopecias. These include other keratin genes for monilethrix, the HR gene for atrichia congenita, the genes CDSN, APCDD1 and SNRPE for the autosomal dominant form of hypotrichosis simplex, and the genes DSG4, LIPH and LPAR6 for the autosomal recessive forms of hypotrichosis as well as U2HR for hypotrichosis type Marie Unna. Molecular genetic and pathophysiological studies of these rare disorders of hair development have significantly contributed to our understanding of the basic mechanisms of hair loss as well as the physiological mechanisms of hair growth.