Search

Amyloid β Protein Precursor Gene and Hereditary Cerebral Hemorrhage with Amyloidosis (Dutch) DEPOSITION OF AMYLOID β PROtein fibrils in the walls of the small vasculature of the leptomeninges and the [...]

Objectives: To describe the consequences of the identification of the Huntington's disease (HD) mutation on predictive and prenatal testing.Methods: A retrospective study was performed considering the test applicants, procedures, and results before and after the identification of the mutation. 1032 people at risk for Huntington's disease in The Netherlands were included, of whom 741 applied for the predictive test in the period 1987 to 1997 in Leiden at the Department of Clinical Genetics, and after 1994, also in the other seven clinical genetics departments in The Netherlands. Uptake, sociodemographic variables, and test results, taken before and after the mutation was identified, are described.Results: The uptake of the predictive test in the period studied was 24% and for the prenatal test 2%. No differences were noted in numbers and sociodemographic data between the period before and after the mutation was identified. After an initial increase in test applicants, a decrease was seen after 1995. After 1993 a significant increase of 25% at risk test applicants and a significant decrease of prenatal exclusion tests was noticed. Only 7% asked for reassessment by mutation analysis. New problems arose after the identification of the mutation, such as the option of reassessing the risk obtained by linkage analysis, direct mutation testing of 25% at risk persons with a parent who does not wish to know, new choices regarding reproduction, and new uncertainties for carriers of intermediate and reduced penetrance alleles and for their offspring and relatives.Conclusions: Although predictive testing has become reliable and available for every person at risk since the mutation has been identified, the uptake of predictive and prenatal tests fell short of expectation, no change in sociodemographic variables was seen, and a decrease in number of applicants was noted. Furthermore, new uncertainties, psychological problems, and questions arose. [ABSTRACT FROM AUTHOR]

To estimate the impact of the Huntington gene on mortality, we studied ten families with Huntington disease, whose records started before 1800. We investigated mortality from 1800 to 1997 in 257 carriers of the Huntington gene and 474 potential carriers. Follow-up extended from age 20 years to the date of death or end-of-study date. The observed deaths were compared with those expected on the basis of the general population, adjusted for sex, age, and calendar time. To study the influence of the family and parental transmission, we calculated hazard ratios adjusted for sex, probability of carrying the gene, and year of birth. In 25,013 person-years, 420 deaths occurred, whereas 278 deaths were expected [standardized mortality ratio = 1.5; 95% confidence interval (CI) = 1.4-1.7]. Excess mortality was confined to ages 40-70 years (standardized mortality ratio = 2.2; 95% CI = 1.9-2.4). To study the evolution of mortality over time in this age group, we calculated absolute mortality rates per calendar period. From 1800 onward, mortality rates in the general population continuously declined, but among the families with Huntington disease this decline was absent. There were only small differences in risk between families, and the relative risk for paternal over maternal transmission was 1.2 (95% CI = 0.9-1.5). Our main finding is that persons who carry the Huntington gene and reach middle age have not benefited from advances in medical care and overall increase in life expectancy.

The candidate region for the Huntington disease (HD) gene has been narrowed down to a 2.2-Mb region between D4S10 and D4S98 on the short arm of chromosome 4. To map the HD gene within this candidate region 65 Dutch HD families were studied. In total 338 informative meioses were analyzed and 11 multiple informative crossovers were detected. Assuming a minimum number of recombinations and no double recombinations, our multiple informative crossovers are consistent with one specific genetic order for 12 loci: D4S10-(D4S81, D4S126)-D4S125-(D4S127,D4S95)-D4S43-(D4 S115, D4S96, D4S111, D4S90, D4S141). This is in agreement with the known data derived from similar and other methods. The loci between brackets could not be mapped relative to each other. In our family material, two informative three-point marker recombination events were detected in the proximal HD candidate region, which are also informative for HD. Both recombination events map the HD gene distal to D4S81 and most likely distal to D4S125, narrowing down the HD candidate region to a 1.7-Mb region between D4S125 and D4S98.

Significant linkage disequilibrium has been found between the Huntington disease (HD) gene and DNA markers located around D4S95 and D4S98. The linkage-disequilibrium studies favor the proximal location of the HD gene, in contrast to the conflicting results of recombination analyses. We have analyzed 45 Dutch HD families with 19 DNA markers and have calculated the strength of linkage disequilibrium. Highly significant linkage disequilibrium has been detected with D4S95, consistent with the studies in other populations. In contrast with most other studies, however, the area of linkage disequilibrium extends from D4S10 proximally to D4S95, covering 1,100 kb. These results confirm that the HD gene most likely maps near D4S95.

Bird et al. (1974) noted an interesting 'anticipation' phenomenon in Huntington's Chorea occurring in patients who inherited the gene from their father. More extensive samples from 165 pedigrees in the Low Countries permitted us to show that most of this apparent 'anticipation' is an artifact due to sampling biases related to the year of birth categories of the affected parents. When these biases were excluded no differences exist between the ages of death of affected mothers and their affected children, but a small difference of approximately two years remains between affected fathers and their affected children. This is explainable by the observation that juvenile cases of Huntington's Chorea usually have inherited the abnormality from their father.

For 1100 patients with Huntington's Chorea in 102 families from The Netherlands the average age at death per family is presented. This average ranges from 72 to 38 years. An analysis of variance of the data is strongly indicative of genetic heterogeneity. For the patients with the relatively high age at death little or no difference is observed from the age at death of their non-affected parents and non-affected sibs. Eleven children who presented with the juvenile form of the disease had all inherited the abnormal gene from their father. These 11 children were found only in families with an average age at death below 57 years. Other factors that might possibly influence the variation of average age at death between families are discussed, but cannot explain the observed differences.

Genetic linkage between the marker G8 (D4S10) and Huntington disease (HD) was studied in six Dutch pedigrees. The informativeness of the D4S10 locus was increased by isolation of a cosmid, C5.5, with a G8 subclone used as probe. We present a restriction map of 70 kb in the D4S10 region. Two subclones of C5.5, H5.52 and F5.53, detect MspI and SinI RFLPs, respectively. These probes increase the informativeness of D4S10 in the Dutch HD population from 55% to 95%. Seven recombinations were found in 124 informative meioses in which multipoint segregation of D4S10 haplotypes and the HD locus was studied. Two of the recombinations occurred within the D4S10 region. The other five recombinations are highly valuable for the mapping of present and future markers relative to each other and to the HD gene. In addition, several recombinations between markers in meioses from unaffected parents were noted, which will also be useful in ordering new markers. On the basis of our three-point recombination data, the orientation of the D4S10 region relative to HD is HD-H5.52-G8-F5.53, which independently confirms the previously derived polarity for D4S10.