Phenotypic characterization of X-linked hypophosphatemia in pediatric Spanish population

Abstract

Deformitats òssies; Retard en el creixement; Hipofosfatèmia hereditària

Deformidades óseas; Retraso en el crecimiento; Hipofosfatemia hereditaria

Bone deformities; Growth retardation; Inherited hypophosphatemia

Background X-linked hypophosphatemia (XLH) is a hereditary rare disease caused by loss-of-function mutations in PHEX gene leading tohypophosphatemia and high renal loss of phosphate. Rickets and growth retardation are the major manifestations of XLH in children, but there is a broad phenotypic variability. Few publications have reported large series of patients. Current data on the clinical spectrum of the disease, the correlation with the underlying gene mutations, and the long-term outcome of patients on conventional treatment are needed, particularly because of the recent availability of new specific medications to treat XLH. Results The RenalTube database was used to retrospectively analyze 48 Spanish patients (15 men) from 39 different families, ranging from 3 months to 8 years and 2 months of age at the time of diagnosis (median age of 2.0 years), and with XLH confirmed by genetic analysis. Bone deformities, radiological signs of active rickets and growth retardation were the most common findings at diagnosis. Mean (± SEM) height was − 1.89 ± 0.19 SDS and 55% (22/40) of patients had height SDS below—2. All cases had hypophosphatemia, serum phosphate being − 2.81 ± 0.11 SDS. Clinical manifestations and severity of the disease were similar in both genders. No genotype—phenotype correlation was found. Conventional treatment did not attenuate growth retardation after a median follow up of 7.42 years (IQR = 11.26; n = 26 patients) and failed to normalize serum concentrations of phosphate. Eleven patients had mild hyperparathyroidism and 8 patients nephrocalcinosis. Conclusions This study shows that growth retardation and rickets were the most prevalent clinical manifestations at diagnosis in a large series of Spanish pediatric patients with XLH confirmed by mutations in the PHEX gene. Traditional treatment with phosphate and vitamin D supplements did not improve height or corrected hypophosphatemia and was associated with a risk of hyperparathyroidism and nephrocalcinosis. The severity of the disease was similar in males and females.

This research has been partially funded by Kyowa Kirin Farmacéutica S.L.U., project PI17/01745 from Instituto de Salud Carlos III, Acción Estratégica en Salud 2017-2020 and FEDER funds, Fondo de Investigaciones Sanitarias (FIS), Fundación Nutrición y Crecimiento (FUNDNYC), Instituto de Investigación Sanitaria del Principado de Asturias (ISPA) and Fundación para la Investigación y la Innovación Biosanitaria del Principado de Asturias (FINBA).