Summary. Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding disorder caused by lack or dysfunction of αIIbβ3 in platelets. GT is relatively frequent in highly inbred populations. We previously identified a 13‐bp deletion in the αIIb gene that causes in‐frame deletion of six amino acids in three Palestinian GT patients. In this study, we determined the molecular basis of GT in all known Palestinian patients, examined whether Jordanian patients harbor the same mutations, analyzed whether there is a founder effect for the 13‐bp deletion, and determined the mechanism by which the 13‐bp deletion abolishes αIIbβ3 surface expression. Of 11 unrelated Palestinian patients, eight were homozygous for the 13‐bp deletion that displayed common ancestry by haplotype analysis, and was estimated to have occurred 300–600 years ago. Expression studies in baby hamster kidney cells showed that substitution of Cys107 or Trp110 located within the deletion caused defective αIIbβ3 maturation. Substitution of Trp110, but not of Cys107, prevented fibrinogen binding. The other Palestinian patients harbored three novel mutations: G2374 deletion in αIIb gene, TT1616‐7 deletion in β3 gene, and IVS14: −3C → G in β3 gene. The latter mutation caused cryptic splicing predicting an extended cytoplasmic tail of β3 and was expressed as dysfunctional αIIbβ3. None of 15 unrelated Jordanian patients carried any of the described mutations.

We examined platelet aggregation in platelet-rich plasma (PRP) and in whole blood in nine patients with Thrombasthenia Glanzmann (TG). In PRP, aggregation was measured by monitoring the changes in light absorbance that occurred in response to adenosine 5-diphosphate (ADP), collagen and ristocetin. To measure platelet aggregation in whole blood, we used multiple electrode Impedance aggregometry using the same aggregating agents. In PRP, the patient's platelets showed defective aggregation in response to ADP, collagen, epinephrine and partially to ristocetin in all patients. In whole blood, platelet aggregation in response to the same aggregating agents showed similar response and appeared to be very similar to that which occurred in PRP. Whole blood impedance aggregometry seems to give similar results to PRP light transmission aggregometry in patients with TG. Multiple electrode aggregometry (MEA) is faster and more convenient to use in these patients.

Cisplatin and carboplatin are integral parts of many antineoplastic management regimens. Both platinum analogues are potent DNA alkylating agents that robustly induce genomic instability and promote apoptosis in tumor cells. Although the mechanism of action of both drugs is similar, cisplatin appears to be more cytotoxic. In this study, the genotoxic potential of cisplatin and carboplatin was compared using chromosomal aberrations (CAs) and sister-chromatid exchange (SCE) assays in cultured human lymphocytes. Results showed that cisplatin and carboplatin induced a significant increase in CAs and SCEs compared to the control group (p<0.01). Levels of induced CAs were similar in both drugs; however, the magnitude of SCEs induced by cisplatin was significantly higher than that induced by carboplatin (p<0.01). With respect to the mitotic and proliferative indices, both cisplatin and carboplatin significantly decreased mitotic index (p<0.01) without affecting the proliferative index (p>0.05). In conclusion, cisplatin was found to be more genotoxic than carboplatin in the SCE assay in cultured human lymphocytes, and that might explain the higher cytotoxicity of cisplatin.

Acute promyelocytic leukemia (APL) of the M3 subtype is characterized by translocation t(15;17) that generates the PML-RARA fusion gene. Depending on the breakpoint position in the PML gene, 3 main fusion transcripts usually result. These breakpoints are bcr1 and bcr3 in introns 6 and 3, respectively, and bcr2 in exon 6. This report describes a rare atypical bcr2 breakpoint in a patient with morphological, cytogenetic and molecular features of APL. The presence of t(15;17) was first revealed by fluorescent in situ hybridization. Molecular analysis by reverse transcription polymerase chain reaction using primers for different PML-RARA junctions showed bands with different sizes compared with those generated from the three classical breakpoints, namely bcr1, bcr2 and bcr3. However, sequence analysis confirmed the presence of a bcr2 transcript with an atypical breakpoint within exon 6. The patient responded well to treatment and is now in complete remission. However, suggesting a favorable prognosis associated with such a rare transcript is difficult as more similar cases are needed to confirm such a conclusion. This article also stresses the importance of sequencing unusual polymerase chain reaction products to confirm their nature.

SummaryαIIbβ3 integrin mediates platelet aggregation following its activation. Its absence or dysfunction causes Glanzmann thrombasthenia (GT), an inherited bleeding disorder that is rare worldwide but relatively frequent in several populations with high rates of consanguinity, including Arabs in Israel and Jordan. Cysteine residues in the β3 epidermal growth factor (EGF) domains are involved in αIIbβ3 formation and activation. In this study we present a novel Cys549Arg mutation in β3 identified in six Jordanian families, which in the homozygous state is manifested by severe GT. The mutation is located in EGF-3 of β3 predicting disruption of a conserved disulfide bond between Cys549 and Cys558. Haplotype analysis disclosed a common founder whose age estimate was 120–150 years. Flow cytometry revealed 1–14% of normal αIIbβ3 expression at the patients' platelet surface. The Cys549Arg or artificial Cys549Ser mutations were introduced into a β3 expression vector. Co-transfection of baby hamster kidney cells with normal or mutant β3 along with normal αIIb demonstrated reduced surface expression of αIIbβ3 by both mutants. The mutants were constitutively active as demonstrated by 20-fold increased binding of the ligand-mimetic antibody PAC-1. Immunoblotting and immunoprecipitation experiments showed reduced β3 and αIIbβ3 expression and a higher than normal ratio of pro-αIIb to mature αIIb. Immunofluorescence experiments showed that β3 and αIIbβ3 were mostly retained in the endoplasmic reticulum. In conclusion, the novel ancestral mutation found in a cluster of Jordanian GT patients disrupts a conserved Cys549-Cys558 bond which results in reduced production of constitutively active αIIbβ3.