Background: Autosomal recessive woolly hair/hypotrichosis (ARWH/H) is caused by mutations in LIPH. Homozygotes for the LIPH c.736T>A (p.C246S) mutation, the most prevalent genotype in Japanese patients, present varying degrees of hair loss; however, determinants of this phenotypic diversity remain elusive. Objectives: To establish methodologies for quantitative assessment of clinical severity and provide a detailed characterization to elucidate the factors contributing to phenotypic divergence. Methods: Digital image analyses were conducted to convert clinical severities into numerical values. Eight patients with ARWH/H were classified into three groups (mild, severe, very severe), based on severity scores. Dermoscopic images were collected and assessed for total hair numbers and hair thickness for intergroup comparisons. Results: The image analysis detected a difference in hair thickness but not in total hair numbers, between mild and severe cases. A marked decrease in total hair number was noted in an atypical very severe case. Histopathologically, a patient with a mild case demonstrated hair miniaturization and a high telogen/anagen ratio without a decrease in total hair count, endorsing dermoscopic observations. Two children demonstrated spontaneous improvement without an increase in total hair numbers, and two adults responded well to topical minoxidil with increased total hair numbers and hair thickness. Conclusions: The difference in the frequency of underdeveloped hairs may be a major factor contributing to the clinical diversity of hair sparseness in LIPH c.736T>A homozygotes with ARWH/H. Hence, pharmacological modification to thicken existing fine hairs may provide a therapeutic strategy.
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