Persistent hyperphosphatasia associated with developmental delay and seizures was described in a single family by Mabry et al. 1970 (OMIM 239300), but the nosology of this condition has remained uncertain ever since. We report on five new patients (two siblings, one offspring of consanguineous parents, and two sporadic patients) that help delineate this distinctive disorder and provide evidence in favor of autosomal recessive inheritance. Common to all five new patients is facial dysmorphism, namely hypertelorism, a broad nasal bridge and a tented mouth. All patients have some degree of brachytelephalangy but the phalangeal shortening varies in position and degree. In all, there is a persistent elevation of alkaline phosphatase activity without any evidence for active bone or liver disease. The degree of hyperphosphatasia varies considerably ( approximately 1.3-20 times the upper age-adjusted reference limit) between patients, but is relatively constant over time. In the first family described by Mabry et al. 1970, at least one member was found to have intracellular inclusions on biopsy of some but not all tissues. This was confirmed in three of our patients, but the inclusions are not always observed and the intracellular storage material has not been identified.
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