Summary
We investigated two unrelated patients with Bernard-Soulier syndrome (BSS) by performing
molecular and genetic analysis.
A flow cytometric and immunoblotting analysis showed GP Ibα to be absent from the
platelet membrane of both patients. Other glycoproteins that formed GP Ib/IX/V complex
were present on the platelets, but in decreased amounts. Therefore, GP Ibα gene from
both cases was sequenced after PCR amplification and subcloning. We identified a homozygous
mutation of a dinucleotide deletion within the TGTG repeat at cDNA number 972 to 975
in GP Ibα gene from Case 1. In Case 2, compound heterozygosity was demonstrated in
GP Ibα 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 frameshift, which created a new termination codon shortly thereafter, and thus lead
to a GP Ibα deficiency on the platelet membrane. Truncated mutant proteins could be
detected in the plasma and platelets of Case 2, but 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 have
an important role on the processing of mutant GP Ibα in megakaryocytes and platelets.
