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H syndrome is a rare autosomal recessive disorder that occurs because of mutations in the SLC29A3 gene, encoding the human equilibrative nucleoside transporter, which is a protein located in endosomes, lysosomes, and mitochondria.1, 2, 3, 4, 5 It was first named by Molho-Pessach et al in 2008.1 To date, fewer than 120 cases of this rare disease have been reported worldwide.5 It is characterized by the presence of hyperpigmented indurated patches with overlying hypertrichosis symmetrically involving the inner aspects of the thighs, which may extend to the posterior aspects of the lower limbs, abdomen, and back, while sparing the knees and buttocks. Other important features of H syndrome include sensorineural hearing loss, hyperglycemia/insulin-dependent diabetes mellitus, heart anomalies, hypogonadism, low height (short stature), and hepatosplenomegaly.1, 2, 3, 4, 5, 6 Currently, many investigators consider H syndrome as a novel form of histiocytosis.4,7 In this case series, 3 cases are reported with findings consistent with H syndrome, in addition to new findings that have not been reported in the literature. All 3 of our patients have low bone mineral density associated with musculoskeletal pain, they also have hypovitaminosis D with secondary hyperparathyroidism, and they responded well to vitamin D supplements.

H syndrome is an autosomal recessive syndrome affecting multiple organ systems with a characteristic skin lesion. It occurs because of a mutation in the SLC29A3 gene.1 The first cases of this extremely rare syndrome were reported in consanguineous families of Arab and Bulgarian descent and described in 2008 by Molho-Pessach et al.2, 3 Approximately 100 cases of H syndrome have been reported worldwide.4 Currently, H syndrome is considered a novel form of histiocytosis.5 The hallmark of this syndrome is the presence of bilateral symmetrical hyperpigmented indurated patches with overlying hypertrichosis, mainly involving the medial aspects of the thighs. Other commonly observed features are sensory neural hearing loss, hypogonadism, heart anomalies, hepatosplenomegaly, insulin-dependent diabetes, short stature, and lymphadenopathy.6 Here we report a case of H syndrome, possibly with new phenotypes not described in previous studies.