A mosaic mutation of phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) in X-linked hypophosphatemic rickets with mild bone phenotypes.

X-linked hypophosphatemic rickets (XLH) is primarily characterized by renal phosphate wasting with hypophosphatemia, short stature, and bone deformity of the leg. Here we present a male case of XLH with relatively mild bone deformity caused by a mosaic mutation of the phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX). Polymerase chain reaction (PCR) direct sequencing revealed a novel in-frame deletion, NM-000444.6:c.671-685del p.Gln224-Ser228del, at exon 6 in PHEX as a mosaic pattern. This mutation was not found in any database and may result in a significant change in higher-order protein structure and function. TA cloning of the PCR product and clone sequencing estimated the mutation allele frequency at 21%. Literature review of the previously reported three cases with novel mosaic mutations in PHEX, together with the present case, suggests that the rates of the mutation allele correlate with phenotype severity to some extent. We initially treated him with nutritional vitamin D supplements and phosphate salts. However, to avoid the development of secondary/tertiary hyperparathyroidism, we had switched nutritional to active vitamin D supplementation with reduced phosphorus salts. The present report contributes to understanding the relationship between the mosaic rate, in addition to the mutation locus, of the PHEX gene, and clinical features of XLH.

[The association of hypocarnitinemia with enteral diets and antiepileptic drugs in children and adults with severe physical and mental disabilities].

OBJECTIVE: To examine the risk factors of hypocarnitinemia and hypocarnitinemic symptoms in children and adults with severe physical and mental disabilities. METHODS: The status of hypocarnitinemia as well as the related symptoms were assessed in a total of 78 children and adults with severe physical and mental disabilities who were admitted to National Hospital Organization Iou National Hospital. Their enteral diets and the medication of antiepileptic drugs were evaluated. RESULTS: Markedly decreased blood carnitine levels were noted in patients undergoing an enteral diet without carnitine supplementation as well as in those receiving a combination of valproate sodium (VPA) and phenobarbital (PB). These hypocarnitinemic patients tended to have more frequent episodes of hypoglycemia and hyperammonemia. CONCLUSIONS: Supplemental L-carnitine is needed in patients receiving an enteral diet free of carnitine, those with combination therapy of VPA and PB under oral feeding conditions, and those who develop hyperammonemia during VPA therapy. Patients who received a carnitine-supplemented enteral diet maintained their serum carnitine levels with a relatively low supplemental dose of carnitine.