Background: Autosomal recessive congenital ichthyosis (ARCI) and ichthyosis syndrome (IS) are rare genetic skin disorders. Objective: To estimate the number of patients with ARCI and IS in Japan and clarify the clinicoepidemiologic features of these diseases. Methods: We performed a nationwide survey of patients treated for ARCI or IS during January 2005-December 2009. We developed diagnostic criteria and conducted a primary survey in a stratified random sample of Japanese hospitals to quantify the number of outpatients and inpatients with ARCI or IS. We performed a secondary survey of clinicoepidemiologic features in positive cases. Results: The estimated number of patients receiving treatment for ARCI and IS during 2005-2009 was 220 (95% confidence interval [CI] 180-260). The estimated disease distribution was as follows: 95 (95% CI 80-110) patients with nonbullous congenital ichthyosiform erythroderma, 30 (95% CI 20-40) with lamellar ichthyosis, 15 (95% CI 10-20) with harlequin ichthyosis, and 85 (95% CI 50-120) with IS. Limitations: Patients with a mild case of the disease might not have visited a dermatology department, potentially causing underestimation of affected patients. Conclusion: We report the estimated number of patients with ARCI and IS in Japan and sex differences in the age distribution.
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