Another Cause of Hyperglyceroluria

Abstract

To the Editor: We read with interest the report of Barić et al (1) on glyceroluria and neonatal hemochromatosis. They state that glyceroluria has also been described in humans as a consequence of urine contamination, in fructose-1,6-diphosphatase deficiency and in glycerol kinase deficiency. Recently, we reported on another cause of hyperglyceroluria, namely a homozygous mutation in the aquaporin 7 gene (2). This disorder was detected in 7 children from 3 families, and in 1 of the mothers. Two of these children (from different families) were asymptomatic, as was the mother with this mutation. Two other children presented learning problems, and the remaining 3 showed delayed (psycho)motor development associated, in 1 or 2 patients, with epilepsy, hypotonia, autism, dolichocephaly, discrete facial dysmorphism, and small testes. One patient had mild proteinuria. Serum thyroid-stimulating hormone, measured in 4 children, was mildly increased or in the upper normal range. Serum thyroid hormone levels were normal except in 1 patient with a mildly decreased free thyroxin. All individuals with the mutation showed a mild platelet secretion defect with reduced ATP secretion. Because 3 of the 8 affected individuals were asymptomatic, it is uncertain whether the neurological and morphological features of the phenotype are part of this disorder. In our experience, this tubular hyperglyceroluria is not so rare because we discovered these 3 families in the course of 6 years.