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Biomedical subjects

G Norbury

Publications and source records attributed to G Norbury.

11 recordsLinked to original sources
PubMed2006

DNA analysis: what and when to request?

Over the last 15 years genetic testing by DNA analysis has expanded enormously both in volume and range due to advances in scientific knowledge and analytical technology. This type of analysis has the potential to provide rapid, cost effective, and accurate diagnostic information but also has its limitations. Some of the changes detected may be of ambiguous consequence and as the knowledge base expands so too does the recognition that other factors can influence the clinical picture. In many cases outcomes may be predicted only on a statistical basis rather than individually. Careful attention should therefore be given to the clinical question that is being addressed before such testing is requested.

DNA↗
PubMed2004

Homozygous hypercholesterolaemia and ezetimibe: a case report.

UNLABELLED: A girl of Indian origin presented with unusual nodules on her hands, and total cholesterol was found to be > 25 mmol/L. The girl had "mild" P664L mutation and total cholesterol levels fell by 38% when she was on a diet and statin therapy. A further reduction of 26% in total cholesterol and 37% in low-density lipoprotein (LDL) was achieved by adding ezetimibe to the treatment. CONCLUSION: A case of homozygous hypercholesterolaemia is reported in order to highlight treatment options such as liver transplantation, LDL-aphaeresis and treatment with ezetimibe.

Anticholesteremic Agents↗
PubMed2003

Immunological and genetic analysis of 65 patients with a clinical suspicion of X linked hyper-IgM.

BACKGROUND: X linked hyper-IgM (XHIM) is a primary immunodeficiency caused by mutations in the tumour necrosis factor superfamily 5 gene, TNFSF5, also known as the CD40 ligand (CD40L) gene. Patients often present with recurrent infections, and confirmation of a diagnosis of XHIM enables appropriate therapeutic interventions, including replacement immunoglobulin, antibiotics, and bone marrow transplantation. AIM: To review and optimise the institution's diagnostic strategy for XHIM. METHOD: Samples from 65 boys were referred to this centre for further investigation of suspected XHIM. The results, which included a flow cytometric whole blood assay for CD40L expression followed by mutation analysis in selected patients, were reviewed. RESULTS: Twenty one patients failed to express CD40L and TNFSF5 mutations were found in 20 of these patients. In contrast, no TNFSF5 mutations were found in 16 patients with weak expression of CD40L. Interestingly, one quarter of patients with confirmed XHIM who had TNFSF5 mutations had low concentrations of IgG, IgA, and IgM. Most of the remaining patients with XHIM had the classic pattern of normal or raised IgM with low concentrations of IgA and IgG. CONCLUSIONS: This study demonstrates the usefulness of the whole blood staining method as a rapid screen to select patients for subsequent TNFSF5 mutation analysis, and shows the benefits of a unified protein/genetic diagnostic strategy.

Adolescent↗
PubMed1998

Genetic pathways of colorectal carcinogenesis rarely involve the PTEN and LKB1 genes outside the inherited hamartoma syndromes.

Germline mutations of the PTEN/MMAC1/TEP and LKB1 genes cause hamartomas to develop in the gastrointestinal tracts of patients with Cowden syndrome and Peutz-Jeghers syndrome, respectively. PTEN mutations may also be responsible for some cases of juvenile polyposis. Histologically, hamartomas appear benign, but there is good evidence that in these syndromes, the hamartomas can progress to colorectal carcinoma. It remains unknown whether or not cancers that develop from hamartomas acquire a spectrum of mutations similar to those in sporadic colon cancers. PTEN and LKB1 are candidate genes for mutations in sporadic colon cancers, either as initiating events in tumorigenesis or providing a selective advantage during tumor growth. Using single-strand conformational polymorphism analysis, we have screened a set of sporadic colon cancers for somatic mutations in PTEN and LKB1. No variants predicted to alter protein function were detected in LKB1, but 1 of 72 cancers showed a somatic mutation in PTEN, together with allele loss. This cancer did not have a detectable APC mutation or allele loss at APC. It remains possible that PTEN and LKB1 are inactivated in other sporadic colon cancers by means such as deletion or promoter methylation. Like BRCA1 and BRCA2, however, it appears that PTEN and LKB1 mutations can cause cancers when present in the germline, but occur rarely in the soma.

AMP-Activated Protein Kinase Kinases↗
PubMed1997

Genotypes at the GluR6 kainate receptor locus are associated with variation in the age of onset of Huntington disease.

Huntington disease (HD) is associated with abnormal expansions of a CAG repeat close to the 5' end of the IT15 gene. We have assembled a set of 293 HD subjects whose ages of onset were known and sized their HD CAG repeats. These repeats accounted for 69% of the variance of age of onset when we used the most parsimonious model, which relates the logarithm of age of onset to a function of CAG repeat number. Since other familial factors have been proposed to influence the age of onset of HD, we have examined a number of candidate loci. The CAG repeat number on normal chromosomes, the delta2642 polymorphism in the HD gene, and apolipoprotein E genotypes did not affect the age of onset of HD. Although mitochondrial energy production defects in HD have led to suggestions that variants in the mitochondrial genome may be associated with clinical variability in HD, this suggestion was not supported by our preliminary experiments that examined the DdeI mitochondrial restriction fragment length polymorphism at position 10,394. Excitotoxicity has been a favored mechanism to explain the cell death in HD, particularly since intrastriatal injection of excitatory amino acids in animals creates HD-like pathology. Accordingly, we investigated the GluR6 kainate receptor. Of the variance in the age of onset of HD that was not accounted for by the CAG repeats, 13% could be attributed to GluR6 genotype variation. These data implicate GluR6-mediated excitotoxicity in the pathogenesis of HD and highlight the potential importance of this process in other polyglutamine repeat expansion diseases.

Adult↗
PubMed1997

Homozygotes and heterozygotes for ciliary neurotrophic factor null alleles do not show earlier onset of Huntington's disease.

The CAG repeat number on Huntington's disease (HD) chromosomes accounts for about 60% of the variance in the age at onset of HD. However, distinct familial factors may also influence the age at onset. HD is associated with loss of medium-sized GABA-ergic striatal output neurons. Intracerebral administration of human ciliary neurotrophic factor (CNTF) protects striatal output neurons in excitotoxic rodent and primate models of HD induced by intrastriatal quinolinic acid injection. We have examined the effect of a common null mutation in the human CNTF gene on the age of onset of HD using a multiple regression approach that takes into account the CAG repeat number on HD chromosomes. We failed to detect an earlier onset of HD in nine homozygotes and 71 heterozygotes with this CNTF mutation compared with 203 homozygotes with wild-type alleles.

Age of Onset↗
PubMed1995

Male neonatal death and progressive weakness and immune deficiency in females: an unknown X linked condition.

We report a family with an undiagnosed X linked condition. The grandmother, two of her three daughters, and one of her grand-daughters have a slowly progressive proximal weakness, brisk reflexes, poor bladder function, static reduced night vision, and IgG2 deficiency. The diagnosis of the three living symptomatic females was "hereditary spastic paraplegia plus". They have lost five male children who died in the neonatal period of severe hypotonia and were of low birth weight. Investigations have not led to a unifying diagnosis: myotonic dystrophy, NARP, and X linked hyper IgM were specifically eliminated. Using the hypothesis that the condition is X linked dominant, haplotype analysis of the family suggests that the disease locus is within Xq26-qter. This entity should be considered in the differential diagnosis of families presenting with severe neonatal hypotonia in males and females with symptoms suggestive of complex hereditary spastic paraplegia.

Adolescent↗
PubMed1992

Specific molecular prenatal diagnosis for the CTG mutation in myotonic dystrophy.

The results of DNA analysis for the specific mutation of myotonic dystrophy are reported in eight pregnancies (two studied retrospectively) in six families. Four results were normal; in the other four, large DNA expansions were found, comparable to the range seen in severely affected children with congenital onset of the disorder. The results agreed with those obtained by linked DNA markers in the six cases where they were available. We conclude that specific molecular prenatal diagnosis of myotonic dystrophy is feasible, and that an abnormal result may also give a guide to possible severity, though this should be interpreted with caution until greater experience is available.

Base Sequence↗