SLC29A3 and H syndrome: H syndrome, caused by autosomal recessive mutations in the SLC29A3 gene that encodes the human equilibrative nucleoside transporter 3 (hENT3), a protein found in endosomes, lysosomes, and mitochondria, is clinically characterized by cutaneous hyperpigmentation, hypertrichosis, hepatosplenomegaly, and hypogonadism as well as heart anomalies [9].