Biomedical subjects

N Risch

Publications and source records attributed to N Risch.

150 records · Page 9Linked to original sources

PubMed1979

Application of a recombination model in calculating the variance of sib pair genetic identity.

Using a previously described model of crossing over (Risch & Lange, 1979), we have calculated analytically the variance in the proportion of genes identical by descent shared by two sibs. The prior distributions for numbers of chiasmata reported in Suarez et al. (1979) were used to calculate a standard deviation of 0.040 for the 22 human autosomes. It is also shown that any two identity by descent values within a sibship are uncorrelated.

Animals↗

PubMed1978

Bacteriochlorophyll cs, a new bacteriochlorophyll from Chloroflexus aurantiacus.

From four strains of the gliding phototrophic bacterium Chloroflexus aurantiacus, the as yet unknown bacteriochlorophyll cs was isolated in addition to small amounts of the known bacteriochlorophyll ap. The new bacteriochlorophyll cs is the main photosynthetic pigment of these organisms under the growth conditions used. It is different from the known bacteriochlorophylls c, as could be shown unequivocally by chromatographic examinations. Evidence for the structure of the new bacteriochlorophyll cs was obtained from mass spectra. The u.v./vis.-spectra and the chromatographic behavior are in accord with the suggested structure. The result includes two particularly interesting aspects: 1. Unlike the bacteriochlorophylls c, d, and e of the Chlorobiaceae, bacteriochlorophyll cs of Chloroflexus is not a mixture of isomeric and homologous molecules; 2. the esterifying alcohol of the propionic acid side chain is neither farnesol nor another isoprenoid alcohol, but is the straight chain aliphatic (C-18) stearylalcohol.

Bacteria↗

PubMed1977

Comments on lack of interference in the four strand model of crossing over.

Assuming a four strand model and no chromatid interference, lack of chiasma interference is known to be equivalent to the assumption that the formation of chiasmata follows a Poisson process. We prove the lack of chiasma interference is also equivalent to the assumption that a random gamete shows recombination on any given interval of a chromosome independently of recombination on all disjoint intervals. Both assumptions are sufficient, but not necessary, for Haldane's formula relating recombination to map distance to be true, as we demonstrate by specific counterexamples. These issues are discussed in the context of the theory of stochastic point processes.

Chromatids↗

PubMedDate not supplied

Age at onset in bipolar-related major affective illness: clinical and genetic implications.

Age-of-onset data were collected on 142 bipolar probands (61 males, 81 females) and 110 siblings. After correcting for demographic factors the age at illness onset did not distinguish bipolar from unipolar siblings or siblings from probands. This indicates that in a subset of pedigree data, bipolar and unipolar affective disorders may be different phenotypic manifestations of the same underlying disorder. A total of 43% of affected individuals gave evidence of illness before age 30 and 11% were ill as adolescents. Also 2% were affected prior to age 15. The data indicate that affective illness is not uncommon in adolescence and may occur as a childhood disorder. Estimation of the age-of-onset probability distribution was obtained by incorporating demographic factors (survivorship data) into the observed ages at onset of affected individuals. A square-root normal curve fits the age-of-onset probability density function. The implications for morbid risk prediction and genetic analysis of affective disorders were discussed.

Adolescent↗

PubMedDate not supplied

Genetic linkage between X-chromosome markers and bipolar affective illness.

A pedigree study shows close linkage of bipolar affective illness (manic depression) to the X-chromosome markers colour blindness and glucose-6-phosphate dehydrogenase deficiency. The maximum lod score ranges from 7.52 (assuming homogeneity) to 9.17 (assuming heterogeneity); that is, the odds in favour of linkage range between 3 X 10(7) to 1 and 10(9) to 1. These results provide confirmation that a major psychiatric disorder can be caused by a single genetic defect. As a possible first step in characterizing the primary genetic abnormality, this finding may have important implications for the aetiology, nosology, pathophysiology and, possibly, prevention and treatment of bipolar affective disorder. It also provides a means for identifying and characterizing homogeneous populations of patients and may help in clarifying aetiological heterogeneity.

Bipolar Disorder↗

PubMedDate not supplied

Effects of age, sex, and ethnicity on the association between apolipoprotein E genotype and Alzheimer disease. A meta-analysis. APOE and Alzheimer Disease Meta Analysis Consortium.

OBJECTIVE: To examine more closely the association between apolipoprotein E (APOE) genotype and Alzheimer disease (AD) by age and sex in populations of various ethnic and racial denominations. DATA SOURCES: Forty research teams contributed data on APOE genotype, sex, age at disease onset, and ethnic background for 5930 patients who met criteria for probable or definite AD and 8607 controls without dementia who were recruited from clinical, community, and brain bank sources. MAIN OUTCOME MEASURES: Odds ratios (ORs) and 95% confidence intervals (CIs) for AD, adjusted for age and study and stratified by major ethnic group (Caucasian, African American, Hispanic, and Japanese) and source, were computed for APOE genotypes epsilon2/epsilon2, epsilon2/epsilon3, epsilon2/epsilon4, epsilon3/epsilon4, and epsilon4/epsilon4 relative to the epsilon3/epsilon3 group. The influence of age and sex on the OR for each genotype was assessed using logistic regression procedures. RESULTS: Among Caucasian subjects from clinic- or autopsy-based studies, the risk of AD was significantly increased for people with genotypes epsilon2/epsilon4 (OR=2.6, 95% CI=1.6-4.0), epsilon3/epsilon4 (OR=3.2, 95% CI=2.8-3.8), and epsilon4/epsilon4 (OR=14.9, 95% CI= 10.8-20.6); whereas, the ORs were decreased for people with genotypes epsilon2/epsilon2 (OR=0.6, 95% CI=0.2-2.0) and epsilon2/epsilon3 (OR=0.6, 95% CI=0.5-0.8). The APOE epsilon4-AD association was weaker among African Americans and Hispanics, but there was significant heterogeneity in ORs among studies of African Americans (P<.03). The APOE epsilon4-AD association in Japanese subjects was stronger than in Caucasian subjects (epsilon3/epsilon4: OR=5.6, 95% CI=3.9-8.0; epsilon4/epsilon4: OR=33.1, 95% CI=13.6-80.5). The epsilon2/epsilon3 genotype appears equally protective across ethnic groups. We also found that among Caucasians, APOE genotype distributions are similar in groups of patients with AD whose diagnoses were determined clinically or by autopsy. In addition, we found that the APOE epsilon4 effect is evident at all ages between 40 and 90 years but diminishes after age 70 years and that the risk of AD associated with a given genotype varies with sex. CONCLUSIONS: The APOE epsilon4 allele represents a major risk factor for AD in all ethnic groups studied, across all ages between 40 and 90 years, and in both men and women. The association between APOE epsilon4 and AD in African Americans requires clarification, and the attenuated effect of APOE epsilon4 in Hispanics should be investigated further.

Adult↗