H syndrome is an autosomal recessive genodermatosis with multisystem involvement caused by mutations in SLC29A3.

We sought to investigate the clinical and molecular findings in 79 patients with this disorder.

A total of 79 patients were included, of which 13 are newly reported cases. Because of the phenotypic similarity and molecular overlap with H syndrome, we included 18 patients with allelic disorders. For 31 patients described by others, data were gathered from the medical literature.

The most common clinical features (>45% of patients) were hyperpigmentation, phalangeal flexion contractures, hearing loss, and short stature. Insulin-dependent diabetes mellitus and lymphadenopathy mimicking Rosai-Dorfman disease were each found in approximately 20%. Additional systemic features were described in less than 15% of cases. Marked interfamilial and intrafamilial clinical variability exists. Twenty mutations have been identified in SLC29A3, with no genotype-phenotype correlation.

In the 31 patients described by others, data were collected from the medical literature.

H syndrome is a multisystemic disease with clinical variability. Consequently, all SLC29A3-related diseases should be considered a single entity. Recognition of the pleomorphic nature of H syndrome is important for diagnosis of additional patients.