Hypo-phosphatasia Eye the Signs of Four Siblings

Dintelmann T., Müller H. L., Lieb W.,
Bayerische Julius-Maximilians-Universität Würzburg, Universitäts-Augenklinik (Würzburg)

Purpose: Hypophosphatasia is a rare inborn metabolic disease characterized by defective bone mineralization due to various mutations in the tissue-non-specific alkaline phosphatase (TNSALP) gene. We describe the ophthalmological findings in four siblings with a mild form of hypophosphatasia.
Patients: A boy and three girls aged 10,9,7 and 6 years showed bilateral cristalline deposits of the conjunctiva and subepithelial corneal deposits near the limbus in the interpalpebral fissure. Visual acuity was full, the anterior segment and fundus otherwise unaffected. Pediatrically the children presented with early loss of deciduous teeth at 2 years of age, low levels of serum ALP and elevated levels of urinary phosphoethanolamine. DNA analysis of the father and the children revealed a mutation at position 361 in the TNSALP-gene that caused the conversion of amino acid GAC (Asp) to GTC (Val). This suggests an autosomal dominant form of inheritance.
Conclusions: The mode of inheritance of hypophospatasia is mainly autosomal recessive, although an autosomal dominant form also is described. The clinical expression is highly variable and the diagnosis of mild forms is often difficult. Here conjunctival and corneal findings may be helpful in view of genetic counselling.

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