D. Hypotrichosis simplex of the scalp
Histopathologic evaluation showed increased telogen hairs and decreased anagen-to-telogen hair ratio in the horizontal section. Only a scant perifollicular infiltrate of histiocytes and lymphocytes was found. Ancillary genetic testing was conducted due to suspicion of familial hypotrichosis after clinicopathological correlation. Whole exome genome testing revealed 2 heterozygous variants in the lanosterol synthase gene (c.812T>C and c.1025T>G). A diagnosis of hypotrichosis simplex of the scalp (OMIM 618275) was made. No effective treatment is available for hypotrichosis simplex and further genetic testing was recommended for her parents.
Hypotrichosis simplex is a group of monogenic isolated alopecias that begins in childhood and progresses with age without spontaneous resolution.1 It was first described by Toribio and colleagues2 in 1974 and features familial hair loss limited to the scalp in the early school years, progressing to almost total alopecia in the patient’s mid-20s. Most of the patients have disease onset at birth or in the first decade of life with an inability to grow long hair. Diffuse hair loss of the scalp without hair shaft abnormalities or other ectodermal involvement, such as nails and teeth, is characteristic; extensive involvement to other body areas has also been reported, including eyebrows, eyelashes, or body hair. The discrepancy between clinical phenotypes may be associated with different underlying genetic variants.