Hypophosphatasia: screening and family investigations in an endogamous Hungarian village

A screening programme for hypophosphatasia was performed in a Hungarian village where a family with the disease had previously been observed. Consanguinity was known to be common in this area. 198 schoolchildren were tested. As to physical signs, low serum alkaline phosphatase activity, and phospho-ethanolamine excretion, 3 homozygotes and 12 heterozygotes of the juvenile type of hypophosphatasia were discovered among them. The families of the positive children were investigated; thus altogether 34 subjects were found to be affected by the disease. Tubular reabsorption of phosphates proved to be decreased in the homozygotes and in about half the heterozygotes. In 4 families a transition between hypophosphatasia and pseudohypophosphatasia, i.e. the typical clinical and biochemical picture without a low serum alkaline phosphatase level, was observed. This suggests that the two conditions belong to the same entity.