Cemaliye Boylu Akyerli

Somatic mosaicism for a MECP2 mutation associated with classic Rett syndrome in a boy

Rett syndrome is a severe neurodevelopmental disorder that arises from mutations in the X-linked MECP2 gene. It is almost exclusively seen in girls due to the predominant occurrence of the mutations on the paternal X-chromosome, and also the early postnatal lethal effect of the disease causing mutations in hemizygous boys. We identified a boy with features of classic Rett syndrome who is mosaic for the truncating MECP2 mutation R270X. Chromosome analysis showed normal karyotype. These results indicate that a MECP2 mutation associated with Rett syndrome in females could lead to a similar phenotype in males as a result of somatic mosaicism.

Polymorphisms of glutathione S-transferase genes (GSTM1, GSTP1 and GSTT1) and bladder cancer susceptibility in the Turkish population

Abstract. We investigated the effect of the GSTM1 and GSTT1 null genotypes, and GSTP1 313 A/G polymorphism on bladder cancer susceptibility in a case control study of 121 bladder cancer patients, and 121 age- and sex-matched controls of the Turkish population. The adjusted odds ratio for age, sex, and smoking status is 1.94 [95% confidence intervals (CI) 1.15–3.26] for the GSTM1 null genotype, and 1.75 (95% CI 1.03–2.99) for the GSTP1 313 A/G or G/G genotypes. GSTT1 was shown not to be associated with bladder cancer. Combination of the two high-risk genotypes, GSTM1 null and GSTP1 313 A/G or G/G, revealed that the risk increases to 3.91-fold (95% CI 1.88–8.13) compared with the combination of the low-risk genotypes of these loci. In individuals with the combined risk factors of cigarette smoking and the GSTM1 null genotype, the risk of bladder cancer is 2.81 times (95% CI 1.23–6.35) that of persons who both carry the GSTM1-present genotype and do not smoke. Similarly, the risk is 2.38-fold (95% CI 1.12–4.95) for the combined GSTP1 313 A/G and G/G genotypes and smoking. These findings support the role for the GSTM1 null and the GSTP1 313 AG or GG genotypes in the development of bladder cancer. Furthermore, gene-gene (GSTM1-GSTP1) and gene-environment (GSTM1-smoking, GSTP1-smoking) interactions increase this risk substantially.

Extremely skewed X‐chromosome inactivation patterns in women with recurrent spontaneous abortion

Background:  The role of extremely skewed X‐chromosome inactivation (XCI) has been questioned in the pathogenesis of recurrent spontaneous abortion (RSA) but the results obtained were conflicting.

Endothelial progenitor cells display clonal restriction in multiple myeloma

BackgroundIn multiple myeloma (MM), increased neoangiogenesis contributes to tumor growth and disease progression. Increased levels of endothelial progenitor cells (EPCs) contribute to neoangiogenesis in MM, and, importantly, covary with disease activity and response to treatment. In order to understand the mechanisms responsible for increased EPC levels and neoangiogenic function in MM, we investigated whether these cells were clonal by determining X-chromosome inactivation (XCI) patterns in female patients by a human androgen receptor assay (HUMARA). In addition, EPCs and bone marrow cells were studied for the presence of clonotypic immunoglobulin heavy-chain (IGH) gene rearrangement, which indicates clonality in B cells; thus, its presence in EPCs would indicate a close genetic link between tumor cells in MM and endothelial cells that provide tumor neovascularization.MethodsA total of twenty-three consecutive patients who had not received chemotherapy were studied. Screening in 18 patients found that 11 displayed allelic AR in peripheral blood mononuclear cells, and these patients were further studied for XCI patterns in EPCs and hair root cells by HUMARA. In 2 patients whose EPCs were clonal by HUMARA, and in an additional 5 new patients, EPCs were studied for IGH gene rearrangement using PCR with family-specific primers for IGH variable genes (VH).ResultsIn 11 patients, analysis of EPCs by HUMARA revealed significant skewing (≥ 77% expression of a single allele) in 64% (n = 7). In 4 of these patients, XCI skewing was extreme (≥ 90% expression of a single allele). In contrast, XCI in hair root cells was random. Furthermore, PCR amplification with VH primers resulted in amplification of the same product in EPCs and bone marrow cells in 71% (n = 5) of 7 patients, while no IGH rearrangement was found in EPCs from healthy controls. In addition, in patients with XCI skewing in EPCs, advanced age was associated with poorer clinical status, unlike patients whose EPCs had random XCI.ConclusionOur results suggest that EPCs in at least a substantial subpopulation of MM patients are related to the neoplastic clone and that this is an important mechanism for upregulation of tumor neovascularization in MM.

Analysis of MYH Tyr165Cys and Gly382Asp variants in childhood leukemias

DNA-repair gene mutations have been suspected as being a predisposing factor in the development of leukemia (Horwitz 1997). Our group identified one of the first examples of a DNA-repair gene mutation to be causally linked to childhood hematological malignancies and neurofibromatosis type I, which involves a homozygous germ-line mutation in the mismatch repair (MMR) gene MLH1 (Ricciardone et al. 1999; Wang et al. 1999). Subsequently, homozygous inactivation of MSH2, another MMR gene, was also found to be associated with early onset leukemia (Whiteside et al. 2002). It is well known that heterozygous germ-line mutations in the MMR pathway genes MLH1, MSH2, PMS2, PMS1, and MSH6 lead to hereditary nonpolyposis colorectal cancer (HNPCC) (Peltomaki 2001). Thus, tumorigenesis through an ‘‘MMR deficiency pathway’’ appears to be associated with two different disease phenotypes which are dependent on the status of the germ-line mutation: (a) HNPCC when the mutation is present on only one allele (heterozygous), and (b) hematological malignancies when the mutation(s) is present on both alleles (homozygous or compound heterozygous). Base excision repair (BER) is another important DNA-repair pathway and plays a significant role in the repair of mutations generated by reactive oxygen species during aerobic metabolism. BER was not linked with any human genetic disorder until recently, when a British family in which three siblings affected by multiple colorectal adenomas and carcinoma was shown to be compound heterozygous for MYH missense variants Tyr165Cys (Y165C) andGly382Asp (G382D) (Al-Tassan et al. 2002). MYH is a homologue of E. coli mutY, and the mutations mentioned above affect residues that are conserved (Tyr82 and Gly253). Tyrosine 82 is predicted to function in mismatch specificity and is located in the pseudo-helix-hairpin-helix (Guan et al. 1998). Adenine glycosylase activity assays of the Tyr82Cys and Gly253Asp mutant proteins with 8-oxoG:A and G:A substrates show that their rate for adenine removal at 37 C is reduced by approximately 98% (Tyr82Cys) and 86% (Gly253Asp) (Al-Tassan et al. 2002). Furthermore, bi-allelic germ-line mutations in MYH were identified in seven unrelated patients with colorectal adenomas (six with colorectal cancer) (Jones et al. 2002). Interestingly, the missense variations Tyr165Cys and Gly382Asp, which significantly reduce the adenine glycosylase activity of MYH protein, were each identified once in a normal control group of 100 British individuals with no history of colorectal adenoma or carcinoma (Al-Tassan et al. 2002). Since a connection between DNA-repair gene mutations and the path to hematological malignancy is now well established, and individuals who carry heterozygous MYH missense mutations Tyr165Cys and Gly382Asp have been documented in a control group (Al-Tassan et al. 2002), we investigated the association between these two MYH missense mutations and childhood leukemia risk.