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M R Hegde

Publications and source records attributed to M R Hegde.

6 recordsLinked to original sources
PubMed2001

Compound heterozygosity at the FMR1 gene.

Individuals affected with Fragile X syndrome are usually characterized at the DNA level by the presence of at least 200 CGG repeats in the 5' untranslated region of the FMR1 gene; this number of repeats is defined as a full mutation. Repeats that number 50-200 usually define those with premutations and are termed unaffected carriers. We report here a compound heterozygous female who carried CGG repeats in the FMR1 gene that fall within the premutation and full mutation ranges. The former appears to have been inherited from the father, whereas the latter is an expansion of the premutation carried by the proband's mother. Therefore, the offspring of the proband will carry a significant risk of being affected with Fragile X syndrome, and the paternal uncle and any cousins should be counselled for being at risk for this syndrome.

DNA Mutational Analysis↗
PubMed2001

Clinical & genetic analysis of four patients with distal upper limb spinal muscular atrophy.

BACKGROUND & OBJECTIVES: Distal upper limb spinal muscular atrophy (SMA) is an uncommon segmental variant of SMA. The condition is usually sporadic, affects males more often than females, and manifests late in the second decade of life, remaining confined to the upper limbs. We examined four patients with this form of SMA in order to determine if they carried homozygous deletion mutations in the survival motor neuron (SMN) or neuronal apoptosis inhibitory protein (NAIP) genes that underlie proximal SMA. METHODS: The four patients with distal upper limb SMA were analysed clinically, electrophysiologically and biochemically. Genomic DNA from each of the patients was analysed by restriction enzyme digestion of polymerase chain reaction (PCR) amplification products, as well single stranded conformation polymorphism (SSCP), to detect deletion events of selected exons of the SMN and NAIP genes. RESULTS: The clinical phenotype of the four patients, together with the biochemical and electrophysiological studies, confirmed a diagnosis of distal upper limb SMA. The molecular studies excluded homozygous deletion mutations in these patients as causative of their phenotype. INTERPRETATION & CONCLUSION: The genetic component underlying distal upper limb SMA appears not to involve mutations that are common in proximal SMA patients. It is possible that genes other than SMN and NAIP may be involved, while somatic mosaicism of SMN gene mutations could be implicated in the segmental nature of distal upper limb SMA.

Adolescent↗
PubMed2000

Hierarchical mutation screening protocol for the BRCA1 gene.

The identification of mutations in the BRCA1 gene poses difficulties in achieving a screening outcome that satisfies the twin needs of speed and accuracy. These needs must also take into account the patient's family history and the statistical evaluation of the probability of detecting a mutation. Given the above, we present here a hierarchical mutation screening strategy that comprises two tiers: first, multiplex heteroduplex and exon 13 duplication analysis; second, exon amplification and direct sequencing using a 96-well tray format. The advantages of this strategy are two-fold: first, the division of analytical tools in order to achieve low and high-resolution mutation screening, respectively; second, a streamlined sequencing approach that leads to a sensitive and rapid assay that reduces labor costs and handling errors. The success of this approach is shown by the identification of a novel deletion mutation in exon 14 of the BRCA1 gene, which was not detected by the more conventional protein truncation assay due to the small size of the predicted truncated protein.

Adult↗
PubMed2000

Null alleles at the Huntington disease locus: implications for diagnostics and CAG repeat instability.

PCR amplification of the CAG repeat in exon 1 of the IT15 gene is routinely undertaken to confirm a clinical diagnosis of Huntington disease (HD) and to provide predictive testing for at-risk relatives of affected individuals. Our studies have detected null alleles on the chromosome carrying the expanded repeat in three of 91 apparently unrelated HD families. Sequence analysis of these alleles has revealed the same mutation event, leading to the juxtaposition of uninterrupted CAG and CCG repeats. These data suggest that a mutation-prone region exists in the IT15 gene bounded by the CAG and CCG repeats and that caution should be exercised in designing primers that anneal to the region bounded by these repeats. Two of the HD families segregated null alleles with expanded uninterrupted CAG repeats at the lower end of the zone of reduced penetrance. The expanded repeats are meiotically unstable in these families, although this instability is within a small range of repeat lengths. The haplotypes of the disease-causing chromosomes in these two families differ, only one of which is similar to that reported previously as being specific for new HD mutations. Finally, no apparent mitotic instability of the uninterrupted CAG repeat was observed in the brain of one of the HD individuals.

Aged↗
PubMed1999

Comparative semi-automated analysis of (CAG) repeats in the Huntington disease gene: use of internal standards.

Huntington disease (HD) belongs to the group of neurodegenerative disorders characterized by unstable expanded trinucleotide repeats. In the case of HD, the expansion of a CAG repeat occurs in the IT15 gene. The detection of the expanded CAG repeats has usually involved the electrophoretic separation of polymerase chain reaction (PCR) amplification products using conventional agarose and acrylamide gel electrophoresis. We have undertaken the comparative analysis of sizing CAG repeats of the IT15 gene using radioactive and fluorescent PCR amplification, and the subsequent separation of these products by slab gel and capillary electrophoresis. The assays have been performed on both cloned and sequenced CAG repeats, as well as genomic DNA from HD patients with a wide range of repeat lengths. The mobility of the CAG repeat amplification products of the IT15 gene is greater using capillary electrophoresis compared to slab gel electrophoresis. The analysis of 40 DNA samples from HD patients indicates that the mobility difference increases with the length of the repeat. However, we have devised an allele ladder for sizing the CAG repeats. This ladder provides a mandatory internal calibration system for diagnostic purposes and enables the confident use of either capillary or slab gel electrophoresis for sizing HD alleles.

Automation↗