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

Research paper by Ulla U Feldt-Rasmussen, Robert R Dobrovolny, Irina I Nazarenko, Martin M Ballegaard, Lis L Hasholt, Ase K AK Rasmussen, Erik I EI Christensen, Soren S SS Sorensen, Flemming F Wibrand, Robert J RJ Desnick

Indexed on: 07 Jun '11Published on: 07 Jun '11Published in: Molecular Genetics and Metabolism



Abstract

Fabry disease, an X-linked lysosomal storage disorder, results from the deficient activity of α-galactosidase A (α-Gal A). In affected males, the clinical diagnosis is confirmed by the markedly decreased α-Gal A activity. However, in female heterozygotes, the α-Gal A activity can range from low to normal due to random X-chromosomal inactivation, and diagnostic confirmation requires identification of the family's α-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 α-Gal A activity, α-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 α-Gal A mutation. Subsequent gene dosage analyses identified a large α-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.