High Prevalence of Nephrocalcinosis in Hypophosphatasia Patients with the ALPL c.1559del Gene Variant.

INTRODUCTION

Hypophosphatasia has been reported to develop nephrocalcinosis, renal stone, and chronic kidney failure. We investigated their renal impairments in the adults with hypophosphatasia to know the phenotype-genotype correlation.

METHODS

We subjected 11 patients with hypophosphatasia who were diagnosed by chance in the routine medical health checkup. Most cases had past history of fracture. Bone mineral density showed low or lower normal limit.

RESULTS

Four of six patients also had high levels of ionized Ca. In subjected six cases, four showed high urinary Ca excretion. Nephrocalcinosis is found in five cases even if the symptoms of hypophosphatasia are mild. Four out of five patients with a mutation of c.1559del in ALPL had nephrocalcinosis and/or kidney stones. One patient already developed hydronephrosis. One of six patients with other mutations showed nephrocalcinosis.

CONCLUSIONS

The phenotype-genotype correlation between renal impairment and c.1559del of ALPL gene was suggested.