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- Creighton, S, et al.
(författare)
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Predictive, pre-natal and diagnostic genetic testing for Huntington's disease : the experience in Canada from 1987 to 2000.
- 2003
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Ingår i: Clinical Genetics. - 0009-9163 .- 1399-0004. ; 63:6, s. 462-75
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Tidskriftsartikel (refereegranskat)abstract
- Predictive and pre-natal testing for Huntington's Disease (HD) has been available since 1987. Initially this was offered by linkage analysis, which was surpassed by the advent of the direct mutation test for HD in 1993. Direct mutation analysis provided an accurate test that not only enhanced predictive and pre-natal testing, but also permitted the diagnostic testing of symptomatic individuals. The objective of this study was to investigate the uptake, utilization, and outcome of predictive, pre-natal and diagnostic testing in Canada from 1987 to April 1, 2000. A retrospective design was used; all Canadian medical genetics centres and their affiliated laboratories offering genetic testing for HD were invited to participate. A total of 15 of 22 centres (68.2%), currently offering or ever having offered genetic testing for HD, responded, providing data on test results, demographics, and clinical history. A total of 1061 predictive tests, 15 pre-natal tests, and 626 diagnostic tests were performed. The uptake for predictive testing was approximately 18% of the estimated at-risk Canadian population, ranging from 12.5% in the Maritimes to 20.7% in British Columbia. There appears to have been a decline in the rate of testing in recent years. Of the predictive tests, 45.0% of individuals were found to have an increased risk, and a preponderance of females (60.2%) sought testing. A greater proportion of those at < or = 25% risk sought predictive testing once direct CAG mutation analysis had become available (10.9% after mutation analysis vs 4.7% before mutation analysis, p = 0.0077). Very few pre-natal tests were requested. Of the 15 pre-natal tests, 12 had an increased risk, resulting in termination of pregnancy in all but one. Diagnostic testing identified 68.5% of individuals to be positive by mutation analysis, while 31.5% of those with HD-like symptoms were not found to have the HD mutation. The positive diagnostic tests included 24.5% of individuals with no known prior family history of HD.
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| 2. |
- Almqvist, E W, et al.
(författare)
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High incidence rate and absent family histories in one quarter of patients newly diagnosed with Huntington disease in British Columbia.
- 2001
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Ingår i: Clinical Genetics. - 0009-9163 .- 1399-0004. ; 60:3, s. 198-205
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Tidskriftsartikel (refereegranskat)abstract
- The advent of the direct mutation test for Huntington disease (HD) has made it possible to identify a previously unrecognized symptomatic population of HD, including those with an atypical presentation or patients without a family history of HD. The present study investigated the uptake of this test in the province of British Columbia (BC), Canada and assessed the incidence rate and rate of identification of new mutations for HD. All symptomatic individuals residing in BC who were referred for the genetic test for HD between 1993 and 2000 (n=205) were analyzed for CAG expansion, baseline demographics and clinical data, and a family history of HD. A total of 141 (or 68.8%) had a CAG expansion > or =36. Of these, almost one-quarter (24.1%) did not have a family history of HD. An extensive chart review revealed that 11 patients (or 7.8%) had reliable information on both parents (who lived well into old age) and therefore possibly could represent new mutations for HD. This indicates a three to four times higher new mutation rate than previously reported. Our findings also show that the yearly incidence rate for HD was 6.9 per million, which is two times higher than previous incidence studies performed prior to the identification of the HD mutation. We also identified five persons with a clinical presentation of HD but without CAG expansion (genocopies) (2.4%).
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| 3. |
- Djoussé, L, et al.
(författare)
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Interaction of normal and expanded CAG repeat sizes influences age at onset of Huntington disease.
- 2003
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Ingår i: American Journal of Medical Genetics. Part A. - : Wiley. - 1552-4825 .- 1552-4833. ; 119A:3, s. 279-82
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Tidskriftsartikel (refereegranskat)abstract
- Huntington disease (HD) is a neurodegenerative disorder caused by the abnormal expansion of CAG repeats in the HD gene on chromosome 4p16.3. Past studies have shown that the size of expanded CAG repeat is inversely associated with age at onset (AO) of HD. It is not known whether the normal Huntington allele size influences the relation between the expanded repeat and AO of HD. Data collected from two independent cohorts were used to test the hypothesis that the unexpanded CAG repeat interacts with the expanded CAG repeat to influence AO of HD. In the New England Huntington Disease Center Without Walls (NEHD) cohort of 221 HD affected persons and in the HD-MAPS cohort of 533 HD affected persons, we found evidence supporting an interaction between the expanded and unexpanded CAG repeat sizes which influences AO of HD (P = 0.08 and 0.07, respectively). The association was statistically significant when both cohorts were combined (P = 0.012). The estimated heritability of the AO residual was 0.56 after adjustment for normal and expanded repeats and their interaction. An analysis of tertiles of repeats sizes revealed that the effect of the normal allele is seen among persons with large HD repeat sizes (47-83). These findings suggest that an increase in the size of the normal repeat may mitigate the expression of the disease among HD affected persons with large expanded CAG repeats.
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