| 1. |
- Tsuang, D, et al.
(author)
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Familial aggregation of psychotic symptoms in Huntington's disease.
- 2000
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In: American Journal of Psychiatry. - : American Psychiatric Association Publishing. - 0002-953X .- 1535-7228. ; 157:12, s. 1955-9
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Journal article (peer-reviewed)abstract
- OBJECTIVE: The mutation responsible for Huntington's disease is an elongated and unstable trinucleotide (CAG) repeat on the short arm of chromosome 4. Psychotic symptoms are more common in patients with Huntington's disease than in the general population. This study explored the relationship of psychosis in Huntington's disease patients with the number of CAG repeats and family history of psychosis.METHOD: Forty-four patients with Huntington's disease, 22 with and 22 without psychotic symptoms, were recruited from two university-affiliated medical genetics clinics in Seattle and Vancouver, B.C. Psychiatric assessments of the subjects were made through chart review, and diagnoses were validated by structured interviews in a subset of patients. The demographic and clinical characteristics of the psychotic and nonpsychotic patients were compared.RESULTS: The two groups did not differ in demographic and clinical characteristics, except that subjects with psychosis were significantly more likely than nonpsychotic subjects to have a first-degree relative with psychosis. In eight of nine families in which Huntington's disease probands with psychosis had a first-degree relative with psychosis, the relative's psychosis co-occurred with Huntington's disease. In the Huntington's disease probands with psychosis, the onset of psychosis correlated with the onset of the neurological symptoms of Huntington's disease, and the age at onset of psychosis was lower in probands with a higher number of CAG repeats.CONCLUSIONS: Patients with Huntington's disease and psychotic symptoms may have a familial predisposition to develop psychosis. This finding suggests that other genetic factors may influence susceptibility to a particular phenotype precipitated by CAG expansion in the Huntington's disease gene.
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| 2. |
- Creighton, S, et al.
(author)
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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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In: Clinical Genetics. - 0009-9163 .- 1399-0004. ; 63:6, s. 462-75
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Journal article (peer-reviewed)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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| 3. |
- Langbehn, D, et al.
(author)
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A new model for prediction of the age of onset and penetrance for Huntington's disease based on CAG length.
- 2004
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In: Clinical Genetics. - : Wiley. - 0009-9163 .- 1399-0004. ; 65:4, s. 267-277
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Journal article (peer-reviewed)abstract
- Huntington's disease (HD) is a neurodegenerative disorder caused by an unstable CAG repeat. For patients at risk, participating in predictive testing and learning of having CAG expansion, a major unanswered question shifts from "Will I get HD?" to "When will it manifest?" Using the largest cohort of HD patients analyzed to date (2913 individuals from 40 centers worldwide), we developed a parametric survival model based on CAG repeat length to predict the probability of neurological disease onset (based on motor neurological symptoms rather than psychiatric onset) at different ages for individual patients. We provide estimated probabilities of onset associated with CAG repeats between 36 and 56 for individuals of any age with narrow confidence intervals. For example, our model predicts a 91% chance that a 40-year-old individual with 42 repeats will have onset by the age of 65, with a 95% confidence interval from 90 to 93%. This model also defines the variability in HD onset that is not attributable to CAG length and provides information concerning CAG-related penetrance rates.
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| 4. |
- Almqvist, E W, et al.
(author)
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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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In: Clinical Genetics. - 0009-9163 .- 1399-0004. ; 60:3, s. 198-205
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Journal article (peer-reviewed)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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| 5. |
- Djoussé, L, et al.
(author)
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Interaction of normal and expanded CAG repeat sizes influences age at onset of Huntington disease.
- 2003
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In: American Journal of Medical Genetics. Part A. - : Wiley. - 1552-4825 .- 1552-4833. ; 119A:3, s. 279-82
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Journal article (peer-reviewed)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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| 6. |
- Falush, D, et al.
(author)
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Measurement of mutational flow implies both a high new-mutation rate for Huntington disease and substantial underascertainment of late-onset cases.
- 2001
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In: American Journal of Human Genetics. - : Elsevier BV. - 0002-9297 .- 1537-6605. ; 68:2, s. 373-85
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Journal article (peer-reviewed)abstract
- We describe a new approach for analysis of the epidemiology of progressive genetic disorders that quantifies the rate of progression of the disease in the population by measuring the mutational flow. The framework is applied to Huntington disease (HD), a dominant neurological disorder caused by the expansion of a CAG-trinucleotide sequence to >35 repeats. The disease is 100% penetrant in individuals with > or = 42 repeats. Measurement of the flow from disease alleles provides a minimum estimate of the flow in the whole population and implies that the new mutation rate for HD in each generation is > or = 10% of currently known cases (95% confidence limits 6%-14%). Analysis of the pattern of flow demonstrates systematic underascertainment for repeat lengths <44. Ascertainment falls to <50% for individuals with 40 repeats and to <5% for individuals with 36-38 repeats. Clinicians should not assume that HD is rare outside known pedigrees or that most cases have onset at age <50 years.
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| 7. |
- Li, Jian-Liang, et al.
(author)
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A genome scan for modifiers of age at onset in Huntington disease : The HD MAPS study.
- 2003
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In: American Journal of Human Genetics. - : Elsevier BV. - 0002-9297 .- 1537-6605. ; 73:3, s. 682-7
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Journal article (peer-reviewed)abstract
- Huntington disease (HD) is caused by the expansion of a CAG repeat within the coding region of a novel gene on 4p16.3. Although the variation in age at onset is partly explained by the size of the expanded repeat, the unexplained variation in age at onset is strongly heritable (h2=0.56), which suggests that other genes modify the age at onset of HD. To identify these modifier loci, we performed a 10-cM density genomewide scan in 629 affected sibling pairs (295 pedigrees and 695 individuals), using ages at onset adjusted for the expanded and normal CAG repeat sizes. Because all those studied were HD affected, estimates of allele sharing identical by descent at and around the HD locus were adjusted by a positionally weighted method to correct for the increased allele sharing at 4p. Suggestive evidence for linkage was found at 4p16 (LOD=1.93), 6p21-23 (LOD=2.29), and 6q24-26 (LOD=2.28), which may be useful for investigation of genes that modify age at onset of HD.
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| 8. |
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