X-linked hypophosphatemia in Polish patients. 2. Analysis of clinical features and genotype-phenotype correlation.

Clinical and molecular data of 59 affected persons from 36 unrelated families with XLH (36 probands and 23 members of their families) were analysed. Characteristic phenotypic features (degree of leg deformities, growth failure, tooth abnormalities, tubular reabsorption of phosphate, serum phosphate and 1,25-dihydroxyvitamin D3 concentrations, head length and hearing defect in some cases) were assessed in relation to the type and localisation of 29 different PHEX gene mutations. The severity of clinical symptoms did not strictly depend upon the type and localisation of the PHEX gene mutation. A hearing defect was correlated with mutations in the beginning fragment, while tooth abnormalities and increased head length with the mutations in the beginning and the terminal fragment of the gene. Phosphate and vitamin D3 supplementation usually slowed progressive growth retardation and leg bowing. Our results point to the probability that alternative splicing occurs in the PHEX gene, producing several active forms of the PHEX protein. Some of them might be involved in bone turnover and dentin formation, others in renal phosphate uptake and vitamin D3 metabolism.