A deep intronic PHEX variant in a large Danish family with hereditary hypophosphatemia and a milder skeletal, but more severe dental phenotype

Hereditary hypophosphatemia (HH) are rare diseases, characterized by excessive renal phosphate wasting, rickets and osteomalacia in growing children, and osteomalacia in adults. There are several types of HH caused by pathogenic variants in a number of different genes. We present a large Danish family consisting of 19 family members with clinically and biochemically hypophosphatamia caused by a previously unreported deep intronic splice variant in PHEX: c.1080-687 A > G (p.?). The affected family members displayed a milder HH phenotype compared with a larger group of individuals with other disease causing PHEX variants. We were able to genetically confirm a diagnosis of X-linked hypophosphatemia (XLH) by genome sequencing intron analysis and in vitro analysis consisting of an exon trapping assay. Our findings emphasize the phenotypic variability of XLH, where this family in general displays a milder phenotype. Furthermore, our findings demonstrate that XLH can be caused by intron variants in PHEX.