FAMILY SCREENING FOR A GLANZMANNS-THROMBASTHENIA MUTATION USING PCR-SSCP

Genetic counselling is often requested in Glanzmann's thrombasthenia, but measurements of GPIIb-IIIa density on platelets are often too inco nclusive to allow a precise assessment of whether prospective parents are obligate heterozygotes for this disease by this measure alone. The recent application of PCR technology to Glanzmann's thrombasthenia ha s resulted in the identification of a large number of mutations, i.e, insertions/deletions, splicing defects, in the genes for both GPIIb an d GPIIIa. Among the reported abnormalities is an intronic G --> A subs titution at the splice donor site of intron 15 in the GPIIb gene of a European gypsy tribe. This gives rise to an abnormal splicing, of an 8 -bp deletion located at the 3' end of exon 15, a reading-frame shift a nd a premature stop codon in the mRNA for GPIIb. In applying PCR-SSCP to the elucidation of the genetic defects of a series of Glanzmann's p atients, we have found the above-cited abnormality in three more gypsy families in France. The presence of the mutation was initially establ ished by sequencing the amplified fragment, and its presence in family members was confirmed by both PCR-SSCP and HphI restriction analysis. Evaluation of the intronic G-->A mutation enabled genetic counselling to prospective parents within these families.