Novel SLC34A3 mutation causing hereditary hypophosphataemic rickets with hypercalciuria in a Gambian family

Three siblings, aged 12, 4 and 2 years, presented at a Gambian clinic with bone deformities. Radiographs of knees and wrists confirmed the presence of florid rickets. The family (including 2 unaffected siblings and the mother) were investigated for hereditary rickets. The three affected siblings had biochemical features of hereditary hypophosphataemic rickets with hypercalciuria (HHRH) with normal plasma calcium and 25-hydroxyvitamin D concentrations, elevated 1,25-dihydroxyvitamin D, hypophosphataemia, hyperphosphaturia and hypercalciuria. At presentation, two of the three affected siblings had an elevated fibroblast growth factor-23 (FGF23) concentration. The mother and clinically unaffected siblings had largely normal biochemistry. Genetic analysis of the SLC34A3 gene, encoding the type IIc sodium-phosphate cotransporter, in DNA samples from the siblings and their mother was conducted. Three single nucleotide polymorphisms (SNPs) S168F, E513V and L599L were identified. E513V and L599L had been previously identified as benign polymorphisms. S168F however, is a previously unreported variant. In silico mutation evaluation predicted that the S168F mutation causes changes in the protein product which are damaging to its function. In addition, the three clinically affected siblings were homozygous in the S168F variant whereas the unaffected family members were carriers. This study describes a biochemical profile and complementary gene data consistent with a rare genetic hypophosphataemic rickets disease in a family from rural Gambia. To our knowledge, this study reports the first cases of HHRH in Africa and describes a novel causal mutation within the SLC34A3 gene.