SLC29A3 gene is mutated in pigmented hypertrichosis with insulin-dependent diabetes mellitus syndrome and interacts with the insulin signaling pathway.

Pigmented hypertrichotic dermatosis with insulin-dependent diabetes (PHID) syndrome is a recently described autosomal recessive disorder associated with predominantly antibody negative, insulin-dependent diabetes mellitus. In order to identify the genetic basis of PHID and study its relationship with glucose metabolism, we performed homozygosity mapping in five unrelated families followed by candidate gene sequencing. Five loss-of-function mutations were identified in the SLC29A3 gene which encodes a member of a highly conserved protein family that transports nucleosides, nucleobases and nucleoside analogue drugs, hENT3. We show that PHID is allelic with a related syndrome without diabetes mellitus, H syndrome. The interaction of SLC29A3 with insulin signaling pathways was then studied using an established model in Drosophila melanogaster. Ubiquitous knockdown of the Drosophila ortholog of hENT3, dENT1 is lethal under stringent conditions; whereas milder knockdown induced scutellar bristle phenotypes similar to those previously reported in the knockdown of the Drosophila ortholog of the Islet gene. A cellular growth assay showed a reduction of cell size/number which could be rescued or enhanced by manipulation of the Drosophila insulin receptor and its downstream signaling effectors, dPI3K and dAkt. In summary, inactivating mutations in SLC29A3 cause a syndromic form of insulin-dependent diabetes in humans and in Drosophila profoundly affect cell size/number through interactions with the insulin signaling pathway. These data suggest that further investigation of the role of SLC29A3 in glucose metabolism is a priority for diabetes research.

Pigmented hypertrichotic dermatosis and insulin dependent diabetes: manifestations of a unique genetic disorder?

A novel pigmented dermatosis was observed in four unrelated boys, three of whom had insulin-dependent diabetes. Three patients were the offspring of consanguineous parents. All four boys had pigmented hypertrichotic patches or induration on the upper inner thighs, with variable involvement of the genitalia, trunk, and limbs. Two boys had episcleritis and orbital proptosis with similar facies and musculoskeletal abnormalities including clinodactyly, flat feet, and short stature. One child had paraaortic and inguinal lymphadenopathy and three patients had an enlarged liver and spleen. A large, swollen pancreas was observed on ultrasound imaging in one patient with insulin dependent diabetes who also had echocardiographic evidence of pericardial inflammation. Three boys had elevated laboratory markers of inflammation. Biopsy specimens from the skin and orbit showed a chronic inflammatory cell infiltrate composed of polyclonal lymphocytes, histiocytes, and plasma cells; fibrosis was observed in two patients, one of whom had previously received radiation therapy to the orbit. Two boys responded to treatment with subcutaneous interferon-alpha, combined with a short course of oral prednisone in the child without diabetes. We believe these inflammatory pigmented skin lesions represent a unique dermatosis associated with diabetes mellitus and systemic disease. The pathogenesis is unknown. The presence of consanguinity in three of four families, and similar dysmorphic features in two boys, suggest a genetic disorder, possibly with autosomal recessive inheritance.