Fine-scale mapping of a locus for severe bipolar mood disorder on chromosome 18p11.3 in the Costa Rican population

We have searched for genes predisposing to bipolar disorder (BP) by studying individuals with the most extreme form of the affected phenotype, BP-I, ascertained from the genetically isolated population of the Central Valley of Costa Rica (CVCR). The results of a previous linkage analysis on two extended CVCR BP-I pedigrees, CR001 and CR004, and of linkage disequilibrium (LD) analyses of a CVCR population sample of BP-I patients implicated a candidate region on 18p11.3. We further investigated this region by creating a physical map and developing 4 new microsatellite and 26 single-nucleotide polymorphism markers for typing in the pedigree and population samples. We report the results of fine-scale association analyses in the population sample, as well as evaluation of haplotypes in pedigree CR001. Our results suggest a candidate region containing six genes but also highlight the complexities of LD mapping of common disorders.

A gene conferring susceptibility to type 2 diabetes in conjunction with obesity is located on chromosome 18p11

Genome-wide nonparametric linkage analysis of 480 sib-pairs affected with type 2 diabetes revealed linkage to a previously unreported susceptibility locus on chromosome 18p11. This result improved with stringent subphenotyping using age- and sex-adjusted BMI, ultimately reaching a logarithm of odds of 3.82 (allele sharing 0.6654) at a point between markers D18S976 and D18S391 when the most obese 20% of the sample was analyzed. Several genes on chromosome 18 have been suggested as metabolic disease candidates, but none of these colocalize with our linkage result. We conclude that our results provide support for the presence of a currently uncharacterized gene on chromosome 18p, certain alleles of which confer increased susceptibility to type 2 diabetes in conjunction with obesity. We additionally observed moderate evidence for linkage to chromosome 1, near marker D1S3462; chromosome 4, near marker D4S2361; chromosome 5, near marker D5S1505; and chromosome 17, near marker D17S1301.

A genome scan for type 2 diabetes susceptibility loci in a genetically isolated population

A total of 896 individuals of Ashkenazi Jewish descent were ascertained in Israel from 267 multiplex families, including 472 sib-pairs affected with type 2 diabetes. A genome-wide scan with average marker spacing of 9.5 cM revealed five regions on four chromosomes (4q, 8q, 14q, and 20q) that exhibited nominal evidence for linkage (P < 0.05). The highest observed nonparametric linkage Z score was 2.41 (equivalent to a logarithm of odds score of 1.26) at marker D4S1501. A maximal signal, with a Z score of 2.05, was observed on chromosome 20 near marker D20S195, and another on 20p near marker D20S103 (Z 1.80). A single marker on chromosome 8 (D8S593) and two adjacent markers on chromosome 14 (D14S749 and D14S605) also attained evidence of linkage. To explore the hypothesis that the signals on chromosomes 4 and 20 are differentially attributable to variation in BMI or age of onset, an ordered subset analysis was conducted. This analysis revealed that only when the families were ranked by BMI (in increasing order) did a subset attain nominal significance, and only for chromosome 4. The findings reported here lend credence to the hypothesis, now supported by four studies of Caucasian populations and most recently by a combined analysis of 1,852 pedigrees, that a type 2 diabetes susceptibility locus resides on chromosome 20q. This population, because of its unique genetic attributes, may facilitate identification of this and other genes contributing to type 2 diabetes.

Assessment of weighting methodology for the National Comorbidity Survey

The authors studied weighting adjustments for the National Comorbidity Survey (1990-1992), a large-scale national epidemiologic investigation of the prevalence, risk factors, and consequences of psychiatric morbidity and comorbidity in the United States. Weighting adjustments for differential selection within households, new construction, unit nonresponse, and poststratification were examined separately and in combination. Specific issues addressed included the magnitude of the bias incurred from ignoring the weights, the added variance from weighting and how well this was predicted by simple formulae, and the performance of methods for trimming the weights. Weights had quite modest effects on point estimates of prevalences but resulted in major increases in variance unless trimmed. The weights after trimming and poststratification appeared to work well. It is suggested that the added variance from weighting be carefully monitored in similar surveys. Alternatives to the use of trimming for controlling variance are worth exploring.