Diagnostic dilemma: a young woman with Fabry disease symptoms, no family history, and a 'sequencing cryptic' alpha-galactosidase a large deletion.

摘要

Fabry disease, an X-linked lysosomal storage disorder, results from the deficient activity of alpha-galactosidase A (alpha-Gal A). In affected males, the clinical diagnosis is confirmed by the markedly decreased alpha-Gal A activity. However, in female heterozygotes, the alpha-Gal A activity can range from low to normal due to random X-chromosomal inactivation, and diagnostic confirmation requires identification of the family's alpha-Gal A gene mutation. In a young female who had occasional acroparesthesias, corneal opacities, and 15 to 50% of the lower limit of normal leukocyte alpha-Gal A activity, alpha-Gal A sequencing in two expert laboratories did not identify a confirmatory mutation, presenting a diagnostic dilemma. A renal biopsy proved diagnostic and renewed efforts to detect an alpha-Gal A mutation. Subsequent gene dosage analyses identified a large alpha-Gal A deletion confirming her heterozygosity, and she was started on enzyme replacement therapy. Thus, gene dosage analyses can detect large deletions (>50bp) in suspect heterozygotes for X-linked and autosomal dominant diseases that are "sequencing cryptic," resolving molecular diagnostic dilemmas.