The same genetic defect in three Tunisian families with Bernard Soulier syndrome: a probable founder Stop mutation in GPIbβ.

GPIbα, GPIbβ, and GPIX are three candidate genes for a rare genetic bleeding disorder named Bernard Soulier syndrome (BSS). These genes are unique in the genome and encode for glycoprotein subunits of the GPIb-IX complex. Quantitative or qualitative deficiency in this complex is often associated with BSS. Here, we report the novel variant of BSS in which Ser23 of GPIbβ is substituted by a Stop codon causing a premature termination of translation, recently described in one family. This genetic defect is revealed in three unrelated BSS patients. The pedigree was determined for two families (F1 and F2) and revealed the homozygosity of the mutation in the two patients and its heterozygosity in parents. In the third family, the patient DNA was heterozygote with the same Ser23 Stop mutation in addition to two missense heterozygote mutations (Asp 51 Gly) and (Ala 55 to Pro). We studied the effect of the Ser23 Stop mutation on the expression of the complex. Our findings confirm that the identified GPIbβ mutation is responsible for the BSS phenotype and hampers the GPIb-IX complex to form on the platelets' surface. Regarding the scarcity of the BSS syndrome, the occurrence of the same mutation in three unrelated families would suggest a BSS founder mutation in Tunisia.