A rare cutaneous disease and a systemic inherited histiocytosis with main characteristics of hyperpigmentation, hypertrichosis, hepatosplenomegaly, heart anomalies, hearing loss, hypogonadism, low height, and occasionally, hyperglycemia/diabetes mellitus. The syndrome becomes clinically apparent mostly during childhood, but cases during infancy and late-onset cases have been reported too. Caused by mutations in SLC29A3 (10q22.2) (encoding a nucleoside transporter, hENT3), which result in defective nucleoside transport functions of hENT3. This leads to histiocytic infiltration of numerous organs. Transmission is autosomal recessive.