Trait components provide tools to dissect the genetic susceptibility of migraine

The commonly used "end diagnosis" phenotype that is adopted in linkage and association studies of complex traits is likely to represent an oversimplified model of the genetic background of a disease. This is also likely to be the case for common types of migraine, for which no convincingly associated genetic variants have been reported. In headache disorders, most genetic studies have used end diagnoses of the International Headache Society (IHS) classification as phenotypes. Here, we introduce an alternative strategy; we use trait components--individual clinical symptoms of migraine--to determine affection status in genomewide linkage analyses of migraine-affected families. We identified linkage between several traits and markers on chromosome 4q24 (highest LOD score under locus heterogeneity [HLOD] 4.52), a locus we previously reported to be linked to the end diagnosis migraine with aura. The pulsation trait identified a novel locus on 17p13 (HLOD 4.65). Additionally, a trait combination phenotype (IHS full criteria) revealed a locus on 18q12 (HLOD 3.29), and the age at onset trait revealed a locus on 4q28 (HLOD 2.99). Furthermore, suggestive or nearly suggestive evidence of linkage to four additional loci was observed with the traits phonophobia (10q22) and aggravation by physical exercise (12q21, 15q14, and Xp21), and, interestingly, these loci have been linked to migraine in previous studies. Our findings suggest that the use of symptom components of migraine instead of the end diagnosis provides a useful tool in stratifying the sample for genetic studies.     

Common variants show predicted polygenic effects on height in the tails of the distribution, except in extremely short individuals

Common genetic variants have been shown to explain a fraction of the inherited variation for many common diseases and quantitative traits, including height, a classic polygenic trait. The extent to which common variation determines the phenotype of highly heritable traits such as height is uncertain, as is the extent to which common variation is relevant to individuals with more extreme phenotypes. To address these questions, we studied 1,214 individuals from the top and bottom extremes of the height distribution (tallest and shortest ∼1.5%), drawn from ∼78,000 individuals from the HUNT and FINRISK cohorts. We found that common variants still influence height at the extremes of the distribution: common variants (49/141) were nominally associated with height in the expected direction more often than is expected by chance (p<5×10⁻²⁸), and the odds ratios in the extreme samples were consistent with the effects estimated previously in population-based data. To examine more closely whether the common variants have the expected effects, we calculated a weighted allele score (WAS), which is a weighted prediction of height for each individual based on the previously estimated effect sizes of the common variants in the overall population. The average WAS is consistent with expectation in the tall individuals, but was not as extreme as expected in the shortest individuals (p<0.006), indicating that some of the short stature is explained by factors other than common genetic variation. The discrepancy was more pronounced (p<10⁻⁶) in the most extreme individuals (height<0.25 percentile). The results at the extreme short tails are consistent with a large number of models incorporating either rare genetic non-additive or rare non-genetic factors that decrease height. We conclude that common genetic variants are associated with height at the extremes as well as across the population, but that additional factors become more prominent at the shorter extreme.     

Zur stellung der Waldtypen im system der Pflanzengesellschaften

Ohne ZusammenfassungManuskript eingegangen am 7.XI.1953.     

Fine mapping of Hyplip1 and the human homolog, a potential locus for FCHL

Familial combined hyperlipidemia (FCHL) is a common genetic dyslipidemia predisposing to premature coronary heart disease (CHD). We previously identified a locus for FCHL on human Chromosome (Chr) 1q21-q23 in 31 Finnish FCHL families. We also mapped a gene for combined hyperlipidemia (Hyplip1) to a potentially orthologous region of mouse Chr 3 in the HcB-19/Dem mouse model of FCHL. The human FCHL locus was, however, originally mapped about 5 Mb telomeric to the synteny border, the centromeric part of which is homologous to mouse Chr 3 and the telomeric part to mouse Chr 1. To further localize the human Hyplip1 homolog and estimate its distance from the peak linkage markers, we fine-mapped the Hyplip1 locus and defined the borders of the region of conserved synteny between human and mouse. This involved establishing a physical map of a bacterial artificial chromosome (BAC) contig across the Hyplip1 locus and hybridizing a set of BACs to both human and mouse chromosomes by fluorescence in situ hybridization (FISH). We narrowed the location of the mouse Hyplip1 gene to a 1.5-cM region that is homologous only with human 1q21 and within approximately 5–10 Mb of the peak marker for linkage to FCHL. FCHL is a complex disorder and this distance may, thus, reflect the well-known problems hampering the mapping of complex disorders. Further studies identifying and sequencing the Hyplip1 gene will show whether the same gene predisposes to hyperlipidemia in human and mouse. Received: 9 September 2000 / Accepted: 30 October 2000     

Assignment of a novel locus for autosomal recessive congenital ichthyosis to chromosome 19p13.1-p13.2

Autosomal recessive congenital ichthyosis (ARCI) is a rare, clinically and genetically heterogeneous genodermatosis. One gene (transglutaminase 1, on 14q11) and one additional locus (on 2q33-35, with an unidentified gene) have been shown to be associated with a lamellar, nonerythrodermic type of ARCI. We performed a genomewide scan, with 370 highly polymorphic microsatellite markers, on five affected individuals from one large Finnish family with nonerythrodermic, nonlamellar ARCI. The only evidence for linkage emerged from markers in a 6.0-cM region on chromosome 19p13.1-2. The maximum two-point LOD score of 7.33 was obtained with the locus D19S252, and multipoint likelihood calculations gave a maximum location score of 5.2. The affected individuals share two common core haplotypes, which makes compound heterozygosity possible. The novel disease locus is the third locus linked to ARCI, supporting previous evidence for genetic heterogeneity of ARCI. This is also the first locus for a nonlamellar, nonerythrodermic phenotype of ARCI.     

Human cationic amino acid transporter gene hCAT-2 is assigned to 8p22 but is not the causative gene in lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is a recessively inherited amino acid disorder characterized by defective efflux of cationic amino acids at the basolateral membrane of the intestinal and renal tubular epithelium. Recently, cDNAs encoding the related proteins hCAT-2A and hCAT-2B have been cloned. These two carrier proteins are most likely the product of the same gene, hCAT-2. Using the hCAT-2B cDNA, we assigned the hCAT-2 gene to chromosome 8p22. Furthermore, by linkage analysis in Finnish LPI families, we ruled out that hCAT-2B is involved in LPI disease. Received: 28 October 1996 / Accepted: 20 January 1997