MOLECULAR AND GENETIC-ANALYSIS OF 2 PATIENTS WITH BERNARD-SOULIER-SYNDROME - IDENTIFICATION OF NEW MUTATIONS IN GLYCOPROTEIN IB-ALPHA GENE

We investigated two unrelated patients with Bernard-Soulier syndrome ( BSS) by performing molecular and genetic analysis. A flow cytometric a nd immunoblotting analysis showed GP Iba to be absent from the platele t membrane of both patients. Other glycoproteins that formed GP Ib/IXV complex were present on the platelets, but in decreased amounts. Ther efore, GP Iba gene from both cases was sequenced after PCR amplificati on and subcloning. We identified a homozygous mutation of a dinucleoti de deletion within the TGTG repeat at cDNA number 972 to 975 in GP Ib alpha gene from Case 1. In Case 2, compound heterozygosity was demonst rated in GP Ib alpha gene; an insertion of a single base (T); at cDNA number 1,418 in one allele, and a deletion of a single base (A) within the 7-adenine repeat at cDNA number 1,438 to 1,444 in another allele. The three new mutations in both patients appeared to cause a frameshi ft, which created a new termination codon shortly thereafter, and thus lead to a GP Iba deficiency on the platelet membrane. Truncated mutan t proteins could be detected in the plasma and platelets of Case 2, bu t not of Case 1. According to these findings, it is thus supposed that the properties and conformation of additional COOH-terminal peptides, which were supposedly synthesized as results of the mutations, may ha ve an important role on the processing of mutant GP Ib alpha in megaka ryocytes and platelets.