A rapid, semiautomated method for apolipoprotein E genotyping

The efficiency of genetic analysis of DNA from aged siblings to detect chromosomal regions implicated in longevity

Studies of the frequencies of different alleles in young adults and aged individuals have implicated several genes, such as ApoE and ACE, in longevity. However such association studies can easily give rise to spurious results through unsuspected population subdivision, and an approach making use of genetic relationships among relatives is desirable. We have studied the effectiveness of non-parametric genetic analysis to detect different types of loci affecting longevity. The non-parametric method has high statistical power to detect infrequent recessive alleles that are required for, or significantly increase the probability of, survival to advanced age. Statistical power is reduced if a proportion of carriers of the alternative allele is allowed to survive. The method is least effective in detecting alleles that occur at low frequency in young individuals and that subsequently experience high mortality, as is the case for carriers of the epsilon4 allele of ApoE. Genotyping errors will also reduce the value of the NPL statistic in a linear fashion with the error rate and the number of loci genotyped. We have also used the method to analyse genotypes of seven highly polymorphic markers near the ApoE gene in a sample of 188 sibships of nonagenarians and centenarians (n=434) and their children (n=124), however no excess sharing of alleles was detected.

Quantitative assessment of apolipoprotein E genotypes by image analysis of PCR-RFLP fragments

Apolipoprotein E (APOE) genotyping usually involves polymerase chain reaction (PCR) and assessment of restriction fragment length polymorphism (RFLP) by gel electrophoresis. We made determination of HhaI restriction endonuclease digestive patterns more objective and improved diagnostic accuracy with a quantitative approach using sensitive DNA stain (SYBR Green) and image analysis of gel patterns. For distinguishing true and partially-digested restriction fragments, band ratios were calculated for the staining intensity of gel patterns from 116 sample runs of 63 human blood specimens. Each of these specimens was independently genotyped for APOE by at least two (and most of them by three) different PCR-RFLP methods. Based on the distribution of band ratios, decision levels were established and used for developing a program for computer-aided interpretation of APOE genotypes (Microsoft Excel software). Appropriateness of the decision levels for band ratios was validated by APOE genotyping of additional 61 specimens. The approach described here is applicable to a variety of other molecular diagnostic techniques that are based on PCR-RFLP or sequence-specific signal amplifications.

Apolipoprotein E4 and Alzheimer's disease in São Paulo-Brazil

Several recently published studies showed the existence of an association between the allele epsilon 4 of the apolipoprotein E and Alzheimer's disease (AD) in developed countries. We examined this association in 55 patients with possible or probable AD and 56 elderly controls referred to outpatient clinics at the "Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo" and "Centro de Saúde Escola da Faculdade de Saúde Pública da Universidade de São Paulo". The allele epsilon 4 was significantly more frequent among patients than controls (20.9% vs 8.9%, p = 0.038). Thirty-six percent of the cases presented with at least one allele epsilon 4 compared with only 17.9% of the controls (p = 0.027). The presence of at least one epsilon 4 allele increased by 2.63 times the risk of subjects being diagnosed as suffering from AD. All three epsilon 4 epsilon 4 patients were male and had a pre-senile onset of the disease. There was no significant difference between senile and pre-senile cases (41.9% vs 29.2%, p = 0.326) nor between men and women (36.0% vs 36.7%, p = 0.959) regarding their risk of being epsilon 4. The age at onset of symptoms did not differ among the different genotype groups, although epsilon 4 epsilon 4 cases showed a consistent trend for earlier onset. When only patients with the diagnosis of "probable AD" were included in the analysis (n = 43), we observed that 22.1% of the alleles were epsilon 4, a rate that was significantly higher than the 8.9% of controls (p = 0.024). This study supports the association between the presence of the epsilon 4 allele and AD and extend this finding to Brazilian patients. Nonetheless, the presence of this allele is not necessary nor sufficient for the development of the disease and it is possible that its contribution to the pathogenesis of the disorder depends on the subject's ethnic group.

Exclusion of linkage to 14q23-24 in a family with Holt-Oram syndrome

Holt-Oram syndrome is an autosomal dominant disorder with congenital heart defects and skeletal malformations of the upper extremities. A patient with a deletion of 14q23-24 and Holt-Oram syndrome has been described. In this report, however, genetic linkage to the 14q23-24 region is excluded in a multigeneration family with five available individuals affected with Holt-Oram syndrome. Familial Holt-Oram syndrome might be different from the syndrome with the 14q23-24 deletion.