The molecular genetic basis of Glanzmann's thrombasthenia in a gypsy population in France: identification of a new mutation on the alpha IIb gene.

Glanzmann's thrombasthenia is a rare inherited bleeding disorder caused by a qualitative or quantitative defect of platelet alpha IIb beta 3. We describe here a new mutation that is the molecular genetic basis of Glanzmann's thrombasthenia in two gypsy families. Our investigation was focused on the alpha IIb gene as a result of biochemical and immunologic analysis of patients' platelets showing undetectable alpha IIb but residual beta 3 levels. The entire alpha IIb cDNA was polymerase chain reaction (PCR) amplified using patients platelet RNA. Sequence analysis showed an 8-bp deletion located at the 3' end of exon 15. This deletion causes a reading-frame shift leading to a premature stop codon and the synthesis of a severely truncated form of alpha IIb. Genomic DNA study showed a G-->A substitution, the Gypsy mutation, at the splice donor site of intron 15. This mutation results in an abnormal splicing occurring at an alternative donor site located 8 bp upstream from the mutation. Based on those results, an allele-specific PCR analysis was developed to allow a rapid identification of the mutation in patients and potential carriers of the gypsy community. This PCR analysis can also be used for genetic counseling and antenatal diagnosis.