A life table for onset of Huntington's chorea

Assessment of the Performance of a Modified Motor Scale as Applied to Juvenile Onset Huntington's Disease

BACKGROUND

Huntington's disease can present at almost any age but traditionally, those with an onset ≤20 years are described as having juvenile onset Huntington's disease (JOHD). They are more likely to have bradykinesia and dystonia earlier in the course of the disease. The Total Motor Score of the Unified Huntington's Disease Rating Scale (UHDRS-TMS) is often used as the principal outcome measure in clinical trials.

OBJECTIVE

To identify a motor scale more suitable for JOHD patients.

METHODS

A working group reviewed the UHDRS-TMS and modified it by adding four further assessment items. Rasch analysis was used to study the performance of the modified scale in 95 patients with a mean age of 19.4 (SD 6.6) years.

RESULTS

The initial analysis showed a significant overall misfit to the Rasch model and a number of individual items displayed poor measurement properties: all items relating to chorea displayed significant misfit due to under-discrimination. Additionally, a number of items displayed disordered response category thresholds, and a large amount of dependency was present within the item set (96 out of 741 pairwise differences = 13%). An iterative process of scale re-structuring and evaluation was then undertaken, with a view to eliminating the largest sources of misfit and generating a set of items that would conform to Rasch model expectations.

CONCLUSION

This post-hoc scale restructuring appears to provide a valid motor score that is psychometrically robust in a JOHD population. This scale restructuring offers a pragmatic solution to measuring motor function in a JOHD population, and it could provide the basis for the further iterative development of a more useful clinical rating scale for patients with JOHD.

Clinical Neurology and Epidemiology of the Major Neurodegenerative Diseases

Neurodegenerative diseases are a common cause of morbidity and cognitive impairment in older adults. Most clinicians who care for the elderly are not trained to diagnose these conditions, perhaps other than typical Alzheimer's disease (AD). Each of these disorders has varied epidemiology, clinical symptomatology, laboratory and neuroimaging features, neuropathology, and management. Thus, it is important that clinicians be able to differentiate and diagnose these conditions accurately. This review summarizes and highlights clinical aspects of several of the most commonly encountered neurodegenerative diseases, including AD, frontotemporal dementia (FTD) and its variants, progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy (MSA), and Huntington's disease (HD). For each condition, we provide a brief overview of the epidemiology, defining clinical symptoms and diagnostic criteria, relevant imaging and laboratory features, genetics, pathology, treatments, and differential diagnosis.

Informativeness of Early Huntington Disease Signs about Gene Status

BACKGROUND

The cohort-level risk of Huntington disease (HD) is related to the age and symptom level of the cohort, but this relationship has not been made precise.

OBJECTIVE

To predict the evolving likelihood of carrying the Huntington disease (HD) gene for at-risk adults using age and sign level.

METHODS

Using data from adults with early signs and symptoms of HD linked to information on genetic status, we use Bayes' theorem to calculate the probability that an undiagnosed individual of a certain age and sign level has an expanded CAG repeat.

RESULTS

Both age and sign levels have substantial influence on the likelihood of HD onset, and the probability of eventual diagnosis changes as those at risk age and exhibit (or fail to exhibit) symptoms. For example, our data suggest that in a cohort of individuals age 26 with a Unified Huntington's Disease Rating Scale (UHDRS) motor score of 7-10 70% of them will carry the HD mutation. For individuals age 56, the same motor score suggests only a 40% chance of carrying the mutation. Early motor signs of HD, overall and the chorea subscore, were highly predictive of disease onset at any age. However, body mass index (BMI) and cognitive performance scores were not as highly predictive.

CONCLUSIONS

These results suggest that if researchers or clinicians are looking for early clues of HD, it may be more foretelling to look at motor rather than cognitive signs. Application of similar approaches could be used with other adult-onset genetic conditions.

Components of the endocannabinoid and dopamine systems are dysregulated in Huntington's disease: analysis of publicly available microarray datasets

The endocannabinoid system (ECS) and the dopaminergic system (DAS) are two major regulators of basal ganglia function. During Huntington's disease (HD) pathogenesis, the expression of genes in both the ECS and DAS is dysregulated. The purpose of this study was to determine the changes that were consistently observed in the ECS and DAS during HD progression in the central nervous system (CNS) and in the periphery in different models of HD and human HD tissue. To do this, we conducted a meta-analysis of differential gene expression in the ECS and DAS using publicly available microarray data. The consolidated data were summarized as observed changes in gene expression (OCGE) using a weighted sum for each gene. In addition, consolidated data were compared to previously published studies that were not available in the gene expression omnibus (GEO) database. The resulting data confirm gene expression changes observed using different approaches and provide novel insights into the consistency between changes observed in human tissue and various models, as well as disease stage- and tissue-specific transcriptional dysregulation in HD. The major implication of the systems-wide data presented here is that therapeutic strategies targeting the ECS or DAS must consider the dynamic changes in gene expression over time and in different body areas, which occur during HD progression and the interconnectedness of the two systems.

Promoters are differentially sensitive to N-terminal mutant huntingtin-mediated transcriptional repression

Huntington’s disease (HD) is a neurodegenerative disorder caused by the inheritance of one mutant copy of the huntingtin gene. Mutant huntingtin protein (mHtt) contains an expanded polyglutamine repeat region near the N-terminus. Cleavage of mHtt releases an N-terminal fragment (N-mHtt) which accumulates in the nucleus. Nuclear accumulation of N-mHtt has been directly associated with cellular toxicity. Decreased transcription is among the earliest detected changes that occur in the brains of HD patients, animal and cellular models of HD. Transcriptional dysregulation may trigger many of the perturbations that occur later in disease progression. An understanding of the effects of mHtt may lead to strategies to slow the progression of HD. Current models of N-mHtt-mediated transcriptional dysregulation suggest that abnormal interactions between N-mHtt and transcription factors impair the ability of these transcription factors to associate at N-mHtt-affected promoters and properly regulate gene expression. We tested various aspects of the current models using two N-mHtt-affected promoters in two cell models of HD using overexpression of known N-mHtt-interacting transcription factors, promoter deletion and mutation analyses and in vitro promoter binding assays. Consequently, we proposed a new model of N-mHtt-mediated transcriptional dysregulation centered on the presence of N-mHtt at promoters. In this model, N-mHtt interacts with multiple partners whose presence and affinity for N-mHtt influence the severity of gene dysregulation. We concluded that simultaneous interaction of N-mHtt with multiple binding partners within the transcriptional machinery would explain the gene-specificity of N-mHtt-mediated transcriptional dysregulation, as well as why some genes are affected early in disease progression while others are affected later. Our model explains why alleviating N-mHtt-mediated transcriptional dysregulation through overexpression of N-mHtt-interacting proteins has proven to be difficult and suggests that the most realistic strategy for restoring gene expression across the spectrum of N-mHtt affected genes is by reducing the amount of soluble nuclear N-mHtt.

Confidence intervals for an effect size measure based on the Mann–Whitney statistic. Part 1: general issues and tail-area-based methods

For two random variables X and Y, theta = Pr[Y > X] + (1/2)Pr[Y = X] is advocated as a general measure of effect size to characterize the degree of separation of their distributions. It is estimated by U/mn, a generalization of the Mann-Whitney U statistic, derived by dividing U by the product of the two sample sizes. It is equivalent to the area under the receiver operating characteristic curve. It is readily visualized in terms of two Gaussian distributions with appropriately separated peaks. The effect of discretization of a continuous variable is explored. Tail-area-based confidence interval methods are developed which can be applied to very small samples or extreme outcomes.

A study of psychiatric morbidity in patients with Huntington's disease, their relatives, and controls. Admissions to psychiatric hospitals in Denmark from 1969 to 1991

Psychiatric morbidity among 74 non-affected first-degree relatives and 93 non-affected second-degree relatives of patients with Huntington's disease (HD) was compared with that of 37 patients with HD and with matched control groups. Due to specific age criteria, the first-degree relatives were at decreased risk and the second-degree relatives at negligible risk of being carriers of the gene for HD. Information on admissions to departments of psychiatry and diagnoses at discharge were obtained for all subjects from a nationwide central register. Psychiatric morbidity was no greater among relatives than among controls, whereas HD patients had significantly more admissions and psychiatric diagnoses than relatives. Growing up with a risk of developing HD does not itself increase the risk of developing psychiatric illness resulting in hospital admission. Severe psychiatric disorders in HD patients were thus most likely to be aetiologically related to the disease process, possibly through a genetic mechanism.

Huntington's disease: predictive testing and the molecular genetics laboratory

We describe the laboratory-related aspects of a series of 40 completed presymptomatic tests for Huntington's disease, using linked DNA markers. Pedigree structure and marker heterozygosity are shown to be important factors, both in the number of laboratory analyses required to give an informative situation and the residual uncertainty of the final estimate. Specific problems encountered by the testing laboratory are described, with possible ways of avoiding them, and the close links required between laboratory and clinical staff are emphasised.

Age at onset and life table risks in genetic counselling for Huntington's disease

Age related genetic risk data for carrying the gene for Huntington's disease in relatives at risk, based on a previously documented life table approach, are presented in a form allowing ready access for use in genetic counselling. Figures are given for first degree relatives and for second degree relatives showing varying age combinations of consultand and intervening parent at risk. Data are also given for the risk of developing Huntington's disease over varying finite periods in relation to age. The availability of this information in tabular form should help those involved in genetic counselling for this disorder in providing accurate risk estimates to relatives; the data are also of importance for combination with genotype information in predictive testing.

Very early onset Huntington's disease: genetic mechanism and risk to siblings

A study of very early onset Huntington's disease (VEOHD) has shown that at least 38% of gene-carrying sibs also develop symptoms before the age of 10, thus improving the genetic risk for those sibs who remain healthy. The prevalence of VEOHD among sibs shows that mutation during spermatogenesis is most unlikely to account for these uncommon cases. The data suggest that two mechanisms contribute to VEOHD: modification by many genes (individually of small effect), and an epigenetic mechanism occurring when transmission is through a series of males.

Age of onset of Huntington's disease in Tasmania

Various aspects of the age of onset of Huntington's disease (HD) were studied using extensive Tasmanian data. The mean age of onset of those born before 1930 was determined. For the total Tasmanian population of HD sufferers, this was 48.3 years. This finding has clinical implications because the most dangerous period for "at risk" individuals is frequently stated to be between 20 and 45 years. The range of age of onset for one very large Tasmanian family (the "Brothers family") is 53 years, from the second to the seventh decade. There were no juvenile-onset cases (onset before 20 years of age) in patients born in Tasmania before 1930. Three juvenile cases have occurred in those born since 1930. Support was found for the observation of paternal transmission in juvenile-onset HD. No support was found for the observation of maternal transmission in late-onset disease (50 years and beyond).

On the estimation of the age at onset distribution in Huntington's chorea using the EM algorithm

Huntington's chorea is a late onset disease of the nervous system whose mode of inheritance conforms to the autosomal dominant model. The present paper shows how the problem of estimating the distribution of age at onset of the disease can be dealt with as an incomplete data problem via the EM algorithm, both in the parametric and non-parametric setting. In this way it is possible to take into account not only the heterozygotes in the population under study who are manifestly affected, but also those who are apparently unaffected. The estimation of the distribution of age at onset of the disease is required for estimating the posterior probability of heterozygosity of the individual at risk using Bayes' theorem. The proposed approach was applied to data derived from a survey carried out on the population of Latium, Italy.

A time-dependent logistic hazard function for modeling variable age of onset in analysis of familial diseases

The paper presents an extension of the regressive logistic models proposed by Bonney [Biometrics 42:611-625, 1986], to address the problems of variable age-of-onset and time-dependent covariates in analysis of familial diseases. This goal is achieved by using failure time data analysis methods, and partitioning the time of follow up in K mutually exclusive intervals. The conditional probability of being affected within the kth interval (k = 1...K) given not affected before represents the hazard function in this discrete formulation. A logistic model is used to specify a regression relationship between this hazard function and a set of explanatory variables including genotype, phenotypes of ancestors, and other covariates which can be time dependent. The probability that a given person either becomes affected within the kth interval (i.e., interval k includes age of onset of the person) or remains unaffected by the end of the kth interval (i.e., interval k includes age at examination of the person) are derived from the general results of failure time data analysis and used for the likelihood formulation. This proposed approach can be used in any genetic segregation and linkage analysis in which a penetrance function needs to be defined. Application of the method to familial leprosy data leads to results consistent with our previous analysis performed using the unified mixed model [Abel and Demenais, Am J Hum Genet 42:256-266, 1988], i.e., the presence of a recessive major gene controlling susceptibility to leprosy. Furthermore, a simulation study shows the capability of the new model to detect major gene effects and to provide accurate parameter estimates in a situation of complete ascertainment.

Predictive testing for Huntington's disease with linked DNA markers

Availability of new DNA markers, more tightly linked to the Huntington's disease (HD) locus than the original G8 (D4S10) probes, has improved predictive accuracy for both presymptomatic and prenatal exclusion testing. 50 predictive tests were carried out on high-risk individuals. 6 of these were on first-trimester chorionic villus biopsy specimens; in 2 cases the HD gene was not transmitted to the fetus while in 4 cases no exclusion could be made. The remaining 44 tests were on adults with either 25 or 50% risk of manifesting the disease; 19 had a greatly increased risk and 25 a substantially decreased risk of HD. Family structures in Scotland are suitable for testing about 75% of potentially affected individuals, and the new generation of DNA markers makes virtually all families fully informative.

Prenatal exclusion testing for Huntington's disease: a problem of too much information

At eight weeks of pregnancy a couple were informed that the prospective father's mother had died of Huntington's disease (HD). There were no living affected members in the immediate family to confirm the diagnosis. By inspection of the local genetic register, it was established that it was indeed HD segregating in the extended family. Genotyping of the prospective mother and father, the father's unaffected father, and his unaffected maternal grandmother was carried out using a battery of polymorphic DNA markers, including a new probe which has a very low recombination rate with the HD locus. Analysis of DNA from a chorionic villus sample taken at 10 weeks of pregnancy showed that the fetus must have inherited a chromosome from its father's affected mother. Its risk of developing HD was 47%. If the genotype of the unaffected maternal grandmother was taken into account, the risk was reduced to 42%. Neither risk was considered acceptable by the prospective parents and the pregnancy was terminated at 12 weeks' gestation. Prospects for future pregnancies are good, with a 50% chance of having a child whose risk of inheriting the HD gene is less than 1.5%. In retrospect it was noted that although genotyping of the maternal grandmother had refined the fetal risk, it had also nearly contributed to an inadvertent and unwanted predictive test for HD on the father. This case makes the point that in prenatal exclusion testing, linkage information must be generated with considerable care.

Genetic linkage between Huntington's disease and D4S10 (G8) in Scottish families

Genetic linkage between Huntington's disease (HD) and polymorphic DNA markers at the D4S10 locus has been investigated in 16 Scottish families. A maximum lod score of 3.499 at a recombination fraction of 0.07 was found, with 95% confidence limits of 0.02 and 0.22. Only one obvious recombinant was detected, and the wide confidence limits probably reflect the large number of unaffected individuals whose risk could only be estimated empirically.

Using survival methods to estimate age-at-onset distributions for genetic diseases with an application to Huntington disease

Two important considerations in genetic disease are the risk of inheriting the gene for a disease and the age-at-onset distribution among those inheriting it. This paper describes the use of survival data analytic methods to estimate these entities. When a sample consists of children and/or siblings of affected individuals, standard life-table methods such as Kaplan-Meier techniques can be applied. The desired estimators are functions of the Kaplan-Meier estimator and their properties are derived using the invariance principle and delta methods. A discussion of the underlying assumptions and estimators of standard errors and mean onset age are given. In an application to Huntington disease, the risk (+/- SE) of inheriting the gene for disease among children of a singly affected parent is estimated to be 0.499 +/- 0.020 and the estimated mean onset age (+/- SE) is 45.6 +/- 0.7.

The motivation of at-risk individuals and their partners in deciding for or against predictive testing for Huntington's disease

Sixty-six percent of the at-risk persons and 74% of the partners in a large survey in Belgium have the intention of making use of predictive testing for Huntington's disease. One third of them, however, have expressed the intention of postponing the final decision for various reasons. The intention to be tested is not at all related to sociodemographic characteristics. A thorough exploration of the reasons for being in favour of or against taking the test reveals that the motivation inspiring this very personal decision is very complex. In the group of at-risk persons, less than half of the variation in the intention to be tested is explained by the role of a series of specific reasons as predictor variables in a regression analysis. The proportion of explained variation is slightly higher in the group of partners. 'To have certainty about my own future' and 'to make arrangements for the future' play a major part in the decision of the total group. 'Making decisions concerning children' and to a larger extent 'informing children about their risk status' are important factors in deciding in favour of the test.

Presymptomatic testing for Huntington's disease. A case complicated by recombination within the D4S10 locus

Presymptomatic testing for Huntington's disease (HD) is possible through the use of restriction fragment length polymorphisms (RFLPs) at the closely linked D4S10 locus. Recombination between the HD and D4S10 loci will occur in 4%-5% of meioses, and is a well-recognised complication of predictive testing. Recombination between RFLPs within the D4S10 locus is a rare event and can usually be ignored. We report a case where such an intra-locus recombination frustrated attempts to predict the chance of a high-risk individual inheriting the HD gene.

New mutation to Huntington's disease

We report a large family with an isolated case of Huntington's disease (HD), which is probably the result of a new mutation. The patient developed clinical signs typical of HD at the age of 36. The clinical course of the patient's disease is documented by several clinical admissions over a period of 14 years at present. The family history is strikingly negative with the parents having been clearly unaffected into their 80s and with 13 older and two younger, living, healthy sibs. Extensive testing of polymorphic markers (blood groups, red cell and serum proteins, HLA antigens) showed no indication of non-paternity, but rather gave strong support to the hypothesis that the proband is a full sib. In addition, DNA typing for several RFLPs known to be closely linked to the HD gene locus indicated that several clearly unaffected sibs share one or the other or both of the patient's haplotypes. This is further evidence in favour of the hypothesis of a new mutation at the HD locus. The posterior probability of a new mutation to HD in the patient exceeds 99%, even if an a priori probability of non-paternity of 10% and a mutation rate of HD of 10(-7) is assumed.

Considerations in using linkage analysis as a presymptomatic test for Huntington's disease

The polymorphic locus D4S10 that is genetically linked to the locus for Huntington's disease (HD) has made possible a presymptomatic test for those at risk. Because the symptoms of this progressively debilitating and fatal illness are not usually manifest until adulthood, the outcome of the test will influence major decisions about career, marriage, and procreation. Several differential diagnoses must be considered before using the test if HD is not confirmed in at least one family member. Review of a large number of pedigrees has shown that 40% of persons at risk do not have appropriate family structure for a linkage test. Furthermore, uncooperative or inaccessible relatives may make this test infeasible for many others who wish to be tested. Linkage phase, which must be known in the affected parent for an informative test, can be determined using one or more of 12 probe-enzyme combinations for D4S10. Although the polymorphism information content (PIC) value for any one RFLP is less than 40%, the PIC value for the haplotype of the two G8 HindIII, pK083 EcoRI, and R7 BglII RFLPs is greater than 88%. We have developed a scheme to incorporate linkage data and age at onset information adjusted for censored observations, sex of affected parent, and familial correlation for age at onset, using the computer program MLINK for calculation of risk of having HD. Simulated experiments showed that proper age at onset adjustment is crucial to the calculation of the probability of risk. A formal presymptomatic testing protocol, including pre- and post-test counselling, psychological testing, and paternity testing is recommended. Many of these considerations are illustrated in several actual test cases.

Huntington's disease: prediction and prevention

The identification of a DNA restriction fragment length polymorphism closely linked to Huntington's disease on the short arm of chromosome 4 has for the first time allowed presymptomatic prediction to be undertaken in first-degree relatives at risk. The late and variable onset of this dominantly inherited disorder makes such prediction a powerful and potentially valuable aid in genetic counselling, but in the absence of effective therapy there are serious ethical reservations concerning such a predictive test. The new developments have stimulated an active and informative debate among professionals and family members on whether and how predictive tests should be used. Guidelines have emerged which should be useful not only for Huntington's disease, but for other serious late-onset neurogenetic disorders. Meanwhile, studies in Wales and elsewhere have not only confirmed the original linkage but have excluded multi-locus heterogeneity as a significant problem. Genetic prediction for the individual at risk remains critically dependent on a suitable family structure, present in only a minority of families in Wales. A more feasible alternative for most families is prenatal exclusion, which can allow risk prediction for a pregnancy without altering the situation for the person at risk. This approach has already been applied in Wales; the experience gained will be useful in full prediction, which is currently being introduced.

Population studies of Huntington's disease in Wales

Long-term surveillance of Huntington's disease families living in South Wales has been undertaken since 1973. We report the updated data on prevalence and births in 101 kindreds. The trend in the births at risk of Huntington's disease has been compared with a control population in North Wales.

An integrated microcomputer system to maintain a genetic register for Huntington disease

A microcomputer program has been designed to maintain a large data base for Huntington disease. This program facilitates such data manipulation as adding, altering, retrieving, deleting, and printing pedigrees. The program is self-contained and has a risk-calculating routine built in which automatically provides both the Mendelian and age-modified risks. This package is capable of printing the pedigrees on a simple printer or, alternatively, creates an output-file which can be used with a dedicated plotting program for drawing the pedigrees and their data on a plotter. The program has a routine which can provide a series of statistical data from the register including age-of-onset, diagnosis, death, and other useful information.

Which factors influence age at onset and rate of progression in Huntington's disease?

Fifty-one families of patients affected with Huntington's chorea were interviewed with respect to age at onset, symptoms at onset and course of the disease. The interview further comprised questions pertinent to line of transmission, socio-economic status, housing, previous illnesses and pregnancy and stillbirth. Since the study was set up as a fishing expedition detailed quantitative information was gathered on many life-style factors including eating, drinking and smoking habits. In adult age onset cases earlier age at onset correlated with lower rate of progression. Line of transmission was of no influence on age at onset in cases with onset above 20 years. No statistically significant relationship was found between any factor studied and age at onset, except for the intake of milk. Higher previous milk intake was associated with earlier ages at onset. This finding is critically discussed. No difference was found between the respective ages at onset of conduct disorders and affective disorders. This suggests that they are both associated with the Huntington gene.

The problem of isolated cases of Huntington's disease in South Wales 1974-1984

A firm diagnosis of Huntington's Disease (HD) is based upon both clinical observation and a positive family history. 192 cases of HD occurred in South Wales over a 10 year period fitting both criteria but an additional 37 patients did not have affected relatives despite detailed enquiries. Twenty-two of these were still thought to have HD on clinical grounds whilst this diagnosis was thought less likely for 15. Definite post-mortem outcomes are known for 7 patients and the clinical diagnosis confirmed on 6 occasions. Details regarding these two groups are presented together with an additional case in which HD was given on the death certificate but a post-mortem revealed a diagnosis of Kufs' disease.

Studies of a DNA marker (G8) genetically linked to Huntington disease in British families

Close genetic linkage has been shown between the DNA sequence G8 (locus D4S10) and 16 British families with Huntington disease using the HindIII, EcoR1, Nci1, and Pst1 polymorphisms detected by G8, and by combining all the polymorphisms to give a combined haplotype. Two recombinants have been detected in these families giving a maximum lod score of 17.60 at a theta of 0.02. These results confirm the originally reported linkage between the loci and provide evidence against significant multilocus heterogeneity for Huntington disease.

Genetic linkage between Huntington's disease and the DNA polymorphism G8 in South Wales families

Analysis of the polymorphism shown by the DNA probe G8 in eight South Wales families with Huntington's disease has confirmed close genetic linkage between this marker and the disorder, the most likely genetic distance being two centimorgans (cM). The closeness of the linkage suggests that G8 may have clinical applications in genetic prediction for this condition.

Age of onset in siblings of persons with juvenile Huntington disease

The age of onset distribution of Huntington disease (HD) has been defined for siblings of patients who exhibit the disease before age 20. The mean age of onset for the siblings of juvenile onset cases is 26.8 years, which is significantly less than the mean age of onset (39.8) observed in siblings of non-juvenile cases. We have shown that the curve for age of onset in the general affected population is significantly different from that of the juvenile sibships. Furthermore, the significant regression equation suggests that the 'expected age of onset' of a sibling can be predicted from a knowledge of the age of onset of the juvenile proband. This information can be used to predict a range of age of onset for those sibs of juvenile patients who are likely to be asymptomatic heterozygotes with DNA polymorphism studies.

Late onset of Huntington's disease

Twenty-five patients with late-onset Huntington's disease were studied; motor impairment appeared at age 50 years or later. The average age at onset of chorea was 57.5 years, with an average age at diagnosis of 63.1 years. Approximately 25% of persons affected by Huntington's disease exhibit late onset. A preponderance of maternal transmission was noted in late-onset Huntington's disease. The clinical features resembled those of mid-life onset Huntington's disease but progressed more slowly. Neuropathological evaluation of two cases reveal less severe neuronal atrophy than for mid-life onset disease.

Huntington's chorea in South Wales: mutation, fertility, and genetic fitness

A study of mutation, biological fitness, and patterns of family building in Huntington's chorea has been carried out, based on a previously reported population study of the disorder in South Wales. No unequivocal new mutation was identified among 101 kindreds containing 418 affected persons, which supports the extreme rarity of mutation in this disorder. Increased values of fertility and fitness were found, both in relation to unaffected relatives and to the general population of the area. The proportion of unmarried persons and pattern of family building was comparable in affected and unaffected subjects, and no correlation with age at onset or mode of clinical presentation could be found.

A genetic register for Huntington's chorea in South Wales

A regional genetic register for Huntington's chorea in South Wales is described, based on previous family studies in this area, which is one of high prevalence for the disorder. The primary role of the register is to help in the efficient delivery of services, including genetic counselling, to affected subjects and relatives, and to monitor changes in the population at risk. The mode of operation of the register is described and the essential importance of strict confidentiality is stressed.

Huntington's Chorea in South Wales. A genetic and epidemiological study

A study of Huntington's Chorea in South Wales has shown a prevalence of 7.61 per 100,000 in the counties of Gwent and Glamorgan, with a total population of 1.7 million. Heterozygote frequency is close to 1 in 5,000. Total ascertainment within this area has been attempted, and experience since conclusion of the study has shown no patients who have been omitted apart from those originating outside the area and those new cases with no living affected relatives. Analysis of migration patterns suggests that around 20% of cases in each generation arise from outside Glamorgan and Gwent and that around 12% of first-degree relatives of indigenous cases have left the area. The survey has formed the initial phase of a long-term prospective study of the disease involving systematic genetic counselling of all high-risk individuals and regular surveillance to monitor possible trends in future prevalence.