CYS209 SER MUTATION IN THE PLATELET MEMBRANE GLYCOPROTEIN IB-ALPHA GENE IS ASSOCIATED WITH BERNARD-SOULIER SYNDROME

Molecular genetic analysis has been performed on a patient with Bernar d-Soulier syndrome (BSS). The patient had characteristically giant pla telets and was deficient in the glycoprotein (GP) Ib/IX/V complex, the von Willebrand factor (vWf) receptor on platelets. Previous studies w ith monoclonal antibodies directed against GP Ib alpha (CD 42b) and GP IX (CD 42a) demonstrated the absence of GP Ib alpha and presence of s mall amounts of GP IX on the surface of the patient's platelets. In th is study the presence of GPV (CD 42d) is also demonstrated. This indic ates a defect in the alpha-subunit of glycoprotein Ib. Therefore polym erase chain reaction (PCR)-amplification of the genomic DNA coding for GP Ib alpha was performed. Nucleotide sequence analysis of the entire coding region of GP Iba revealed a homozygous single base pair mutati on T --> A, leading to a single amino acid substitution cysteine --> s erine at position 209 of the mature protein. We took advantage of the Mse I target site in the mutant allele, created by the T --> A mutatio n, to analyse all available family members. PCR-ASRA (allele-specific restriction enzyme analysis) using the restriction enzyme Mse I, revea led the heterozygosity of the mother and the two children of the patie nt, whereas homozygosity of the patient for the Cys209Ser mutation was confirmed. The sister of the patient was not found to be a carrier of the mutant allele. The mutation identified in the family studied, res ponsible for the deficiency of the GP Ib/IX/V complex, suggests that t he cysteine at amino acid position 209 may be involved in disulphide b onding.