SVA retrotransposition in exon 6 of the coagulation factor IX gene causing severe hemophilia B.

Hemophilia B is an X-linked recessive bleeding disorder caused by abnormalities of the coagulation factor IX gene (F9). Insertion mutations in F9 ranging from a few to more than 100 base pairs account for only a few percent of all hemophilia B cases. We investigated F9 to elucidate genetic abnormalities causing severe hemophilia B in a Japanese subject. We performed PCR-mediated analysis of F9 and identified a large insertion in exon 6. Next, we carried out direct sequencing of a PCR clone of the whole insert using nested deletion by exonuclease III and S1 nuclease. We identified an approximately 2.5-kb SINE-VNTR-Alu (SVA)-F element flanked by 15-bp duplications in the antisense orientation in exon 6. Additionally, we carried out exontrap analysis to assess the effect of this retrotransposition on mRNA splicing. We observed that regular splicing at exons 5 and 6 of F9 was disturbed by the SVA retrotransposition, suggesting that abnormal FIX mRNA may be reduced by nonsense-mediated mRNA decay. In conclusion, this is the first report of SVA retrotransposition causing severe hemophilia B; only five cases of LINE-1 or Alu retrotranspositions in F9 have been reported previously.

Localized amyloidosis at the site of repeated insulin injection in a diabetic patient.

A 60-year-old woman diabetic patient presented with a subcutaneous mass in right lower abdominal quadrant where recombinant human insulin or insulin analogue had been injected for 16 years. Her diabetes has been insulin resistant with insufficient blood glucose control. The mass was extirpated under the suspicion of neoplasm but it was found to consist of diffuse deposition of eosinophilic amorphous materials mixed with inflammatory change. Congo-red staining demonstrated positive red color and yielded green birefringence by polarized microscopy. Pre-digestion with potassium permanganate was incomplete to quench positive Congo-red stains. Immunostains with insulin antibody were positive for this deposition but not so with amylin or AA or AL amyloid. Thus, the mass was considered to be localized amyloidosis composed of iatrogenic A-Ins type amyloid. Thus, the case suggested that her insulin resistance, i.e. refractoriness of insulin treatment, may be ascribed to poor penetration of injected insulin and human insulin itself or its analogue is amyloidogenic to form a local mass.