Two Mutations (1717 T〉C, GP IX;124del145, GPIb beta) Occur Frequently among Patients with Bernard Soulier Syndrome in India.

Abstract

Bernard Soulier syndrome (BSS) is a rare (1:1000000) hereditary bleeding disorder of platelet adhesion, caused by a qualitative or quantitative defect of glycoprotein (GP)Ib/IX/V complex. We report here the molecular basis of BSS in eight unrelated patients from India. The diagnosis was based on low platelet count, presence of giant platelets and aggregometry studies (absence of response to ristocetin) in eight unrelated patients who presented with mucocutaneous bleeding at 17.9 years of age (range:9 months–60yrs). Flow cytometry to assess surface GPIb/IX/V complex using anti CD42b antibodies showed reduced (7.7%–21.1%, n=6) expression. Genomic DNA was screened for mutations in the GPIb alpha, GPIb beta, GP IX genes by a novel PCR and conformation sensitive gel electrophoresis method. Mutations were identified in all the 8 patients. Six different mutations, including missense (n=4) mutations, a deletion and a duplication were identified of which 5 are novel. Three novel missense mutations were identified in a patient (CD42b:21.1%) of which, Tyr492His in GPIb alpha gene was in heterozygosity and the Glu129His, Leu132Pro mutations in GPIb beta was detected in a double homozygous condition. All these substitutions occur at a highly conserved codon in the transmembrane region of GPIb alpha and beta chains, a region critical for anchoring the glycoprotein subunits into the platelet membrane. A novel homozygous deletion of 22 bp in exon 2 of GPIb beta (124del145, p.Arg17CysfsX14) gene was identified in 3 different patients (CD42b: range, 10.6–15.9%). This deletion occurs at a sequence flanking the leucine rich repeat at the NH2-side of GPIb beta protein results in a premature termination of translation (PTC) and a truncated mutant with 30 amino acids. A novel homozygous duplication of 38 nucleotides (2119_2120 dup38) in the transmembrane region resulted in a frameshift (142AlafsX76) in one of the patient. This frameshift predicts termination after the addition of 75 amino acids. A previously reported homozygous transition (1717 T >C) in the GP IX gene resulting in a Cys8Arg substitution was identified in the remaining 3 patients (CD42b:10.02%, 7.7%). The frequent presence of GP IX 1717 T>C and GPIb beta 124del145 in 6 out of 8 (75%) patients studied, suggests that this could be due to a founder effect. This data adds significantly to the mutation database of this condition and will be useful for genetic diagnosis of this condition in India.