Molecular heterogeneity of the glucose-6-phosphate dehydrogenase deficiency in the Hellenic population

We report results from a systematic study to identify the molecular basis of glucose-6-phosphate dehydrogenase (G6PD) deficiency on a sample of 299 male subjects from the Hellenic population. Our stepwise approach involved partial biochemical characterization and quantitation of the enzyme's activity, MboII restriction endonuclease digestion to identify the G6PD Mediterranean variant, which represents the most frequent G6PD variant in our population and a nonradioactive polymerase chain reaction-single-strand conformation polymorphism methodology for the detection of the underlying molecular defect(s) in the rest of the non-Mediterranean G6PD-deficient individuals. Through this approach, six different G6PD variants were identified (G6PD Mediterranean, G6PD Hermoupolis, G6PD Cassano, G6PD Seattle, G6PD Ierapetra and G6PD Acrokorinthos), two of which were new (G6PD Hermoupolis, G6PD Acrokorinthos). In essence, this study underlines the remarkable genetic heterogeneity of the G6PD deficiency in the Hellenic population, while the finding of the double mutant, G6PD Hermoupolis, may help to outline the relationship and evolution of mutations in the human G6PD locus.

Modification of human beta-globin locus PAC clones by homologous recombination in Escherichia coli

We report here modifications of human beta-globin PAC clones by homologous recombination in Escherichia coli DH10B, utilising a plasmid temperature sensitive for replication, the recA gene and a wild-type copy of the rpsL gene which allows for an efficient selection for plasmid loss in this host. High frequencies of recombination are observed even with very small lengths of homology and the method has general utility for introducing insertions, deletions and point mutations. No rearrangements were detected with the exception of one highly repetitive genomic sequence when either the E.COLI: RecA- or the lambdoid phage encoded RecT and RecE-dependent recombination systems were used.

A novel 23-bp deletion in exon 5 of the p53 tumor suppressor gene

We report a novel p53 deletion in a 63-year-old female with breast cancer. Mutation screening of DNA samples, obtained from tumor specimens from 98 individuals with breast cancer, by a combined polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) analysis showed that the index case had a somatic mutation identified to be a 23-bp deletion in exon 5 of the p53 gene. This deletion would be expected to yield a truncated and functionally inactive p53 protein molecule, probably resulting in cell transformation. The existence of 6-bp palindromic-like sequences encompassing the deleted fragment suggests that the slipped mispairing mechanism is not involved in producing the deletion, which probably resulted from palindromic pairing during replication.

Contribution of gene conversion in the evolution of the human beta-like globin gene family

Gene conversion is referred to as one of two types of mechanisms known to act on gene families, mainly to maintain their sequence homogeneity or, in certain cases, to produce sequence diversity. The concept of gene conversion was established 20 years ago by researchers working with fungi. A few years later, gene conversion was also observed in the human genome, i.e. the gamma-globin locus. The aim of this article is to emphasize the role of genetic recombination, particularly of gene conversion, in the evolution of the human beta-like globin genes and further to summarize its contribution to the convergent evolution of the fetal globin genes. Finally, this article attempts to re-examine the origin and spread of specific mutations of the beta-globin cluster, such as the sickle cell or beta-thalassemia mutations, on the basis of repeated gene conversion events.

The Cretan type of non-deletional hereditary persistence of fetal hemoglobin [A gamma-158C-->T] results from two independent gene conversion events

We report a new type of non-deletional hereditary persistence of fetal hemoglobin that is due to a C-->T transition at position -158, relative to the Cap site of the human Agamma-globin gene. This mutation was identified in three unrelated adult cases presenting slightly elevated levels of fetal hemoglobin (Hb F), i.e. 2.9-5.1%, and normal hematological indices. Our sequencing results, from both polymerase chain reaction-amplified and subcloned DNA fragments, indicate that the A gamma -158C-->T mutation occurred by two independent gene conversion events in the three cases studied. In addition, hematological and molecular data, including restriction fragment length polymorphism haplotyping in the beta-globin gene cluster, extended haplotype analysis inside the gamma-globin gene region and routine analysis of three tandem repeat loci (D1S80, 3'HVR/apoB and F8vWf), led us to conclude that the A gamma -158C-->T mutation in one of the three cases occurred recently in the parental germ line (P=99.47%), representing the first example of a de novo gene conversion event identified in humans.

A new base substitution in the 5' regulatory region of the human Agamma globin gene is linked with the betaS gene

A new T --> A base substitution, identified inside the 5' regulatory region of the human Agamma globin gene (Agamma-499 T -->A), is reported. This nucleotide change was found to be linked in cis with the mutation producing sickle cell anemia (CD6 GAG-->GTG: betaS gene).

HbF-Lesvos: an HbF variant due to a novel G gamma mutation (:G gamma 75 ATA-->ACA) detected in a Greek family

A T-->C substitution at position 402 of the G gamma globin gene results in an isoleucine to threonine substitution at codon 75 of the G gamma globin chain and the formation of HbF-Lesvos [alpha2 G gamma2 75 (E19) Ile-->Thr].