A novel homozygous mutation in LSS gene possibly causes hypotrichosis simplex in two siblings of a Tibetan family from the western Sichuan province of China

Aim: Hypotrichosis simplex (MIM 146520) is a rare form of monogenic hereditary alopecia. Several genes have been identified as being associated with the disease, including LPAR6, LIPH, and DSG4. LSS encoding lanosterol synthase (LSS) has been shown to cause hypotrichosis simplex, but the related mechanisms have not been elucidated to date. This study aims to find mutations in LSS from a Chinese family, among which a 21-year-old male patient and his 9-year-old sister were affected by hypotrichosis simplex. Methods: Dermoscopy and histological analysis were used to examine patients' scalps, while exome sequencing was used to find the mutations in LSS. Results: The hair loss was only detected on the scalp of the proband and his sister, while other ectodermal structures were normal with no systemic abnormalities. Further, the exome sequencing identified a new homozygous mutation NM_002340.6 (LSS_v001):c.812T>C (p.(Ile271Thr)) in the LSS gene of the proband, which was also found in his sister. In addition, a heterozygous mutation of LSS was found in their asymptomatic parents. Finally, the possible protein structure of the mutational LSS was predicted. Conclusion: The hypotrichosis simplex reported here could be an autosomal recessive disease in this family. The mutation on LSS might reduce the enzyme activity of LSS, thus leading to the disease.