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2009 Vienna - European Society of Human Genetics

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Statistical genetics, includes Mapping, linkage and association methods<br />

P08.39<br />

Leptin and leptin receptor gene variation and human obesity<br />

Ž. Tomas 1 , N. Smolej Narančić 1 , M. Barbalić 1 , M. Zajc 1 , T. Škarić-Jurić 1 , P.<br />

Rudan 1 , I. Rudan 2,3 , H. Campbell 3 , A. F. Wright 4 ;<br />

1 Institute for Anthropological Research, Zagreb, Croatia, 2 Croatian Center for<br />

Global Health, Faculty <strong>of</strong> Medicine, University <strong>of</strong> Split, Split, Croatia, 3 Community<br />

Health Sciences, University <strong>of</strong> Edinburgh, Medical School, Edinburgh,<br />

United Kingdom, 4 MRC <strong>Human</strong> <strong>Genetics</strong> Unit, Western General Hospital, Edinburgh,<br />

United Kingdom.<br />

Leptin is a protein hormone with important role in regulation <strong>of</strong> body<br />

weight, metabolism, reproductive function, modulation <strong>of</strong> immune response<br />

and angiogenesis. As a regulator <strong>of</strong> body weight, it operates by<br />

inhibiting food intake and stimulating energy expenditure and its concentration<br />

in the blood serum is proportional to the amount <strong>of</strong> body fat.<br />

Polymorphic leptin and leptin receptor genes have <strong>of</strong>ten been investigated<br />

as possible factors associated with human obesity. We tested<br />

polymorphisms G-2548A in the promoter region and A19G in exon 1<br />

<strong>of</strong> the leptin gene and polymorphisms G-1041A in the promoter region,<br />

Arg109Lys in exon 4 and Arg223Gln in exon 6 <strong>of</strong> the leptin receptor<br />

gene for association with leptin concentration and obesity. Allelic frequencies<br />

<strong>of</strong> these polymorphisms show inter-poplational variation. A<br />

population-based association study was conducted in the population<br />

isolate <strong>of</strong> the Eastern Adriatic island <strong>of</strong> Vis, Croatia (N=243, age 22-<br />

85 yrs). Obesity was defined as BMI≥30 kg/m 2 . Leptin concentration<br />

was significantly higher in the obese (65.3 ng/ml), than in the nonobese<br />

(19.9 ng/ml) and in women (44.6 ng/ml) compared to men (13.8<br />

ng/ml). The results indicated significant association <strong>of</strong> -2548G variant<br />

and leptin concentration in men (p=0.013). No association <strong>of</strong> the other<br />

studied polymorphisms with leptin concentration was found, and none<br />

<strong>of</strong> the studied polymorphisms showed association with obesity (with<br />

leptin concentration, sex and age as covariates). The lack <strong>of</strong> association<br />

could be due to the complex pathogenesis <strong>of</strong> obesity, which<br />

involves a number <strong>of</strong> genetic and environmental factors.<br />

P08.40<br />

statistical properties <strong>of</strong> tests <strong>of</strong> association performed on<br />

mixtures <strong>of</strong> singletons and related individuals: effects <strong>of</strong> the<br />

nonorthogonality <strong>of</strong> linkage and LD parameters on type i error<br />

and power<br />

T. Hiekkalinna 1,2 , L. Peltonen 3,2 , J. Terwilliger 4,2 ;<br />

1 National Institute for Health and Welfare, Helsinki, Finland, 2 Institute for Molecular<br />

Medicine Finland FIMM, Helsinki, Finland, 3 Welcome Trust Sanger<br />

Institute, Hinxton, Cambridge, United Kingdom, 4 Department <strong>of</strong> <strong>Genetics</strong> and<br />

Development, Columbia University, New York, NY, United States.<br />

The current trend in mapping <strong>of</strong> the complex diseases is genome-wide<br />

association by analyzing anonymous SNP markers in cohorts <strong>of</strong> unrelated<br />

cases and controls. A motivation for this is that unrelated individuals<br />

sharing some phenotype are much easier to collect than large<br />

families with multiple affected persons, when the genetic portion <strong>of</strong> the<br />

phenotypic etiology is incomplete.<br />

In this study, we examined the statistical properties <strong>of</strong> several commonly<br />

used family-based association tests in genetic epidemiology as<br />

to their performance using real-life mixtures <strong>of</strong> families and singletons<br />

taken from our own migraine and schizophrenia studies. We simulated<br />

a disease conditional on the known phenotype structures in these pedigrees<br />

under a variety <strong>of</strong> inheritance models in which one variant in a<br />

given gene region influences the trait to some degree.<br />

The results <strong>of</strong> our study showed the in virtually every situation, the full<br />

likelihood-based methods outperformed the simpler “data structuremotivated”<br />

tests. In truth we never know the true analysis models, so<br />

we noticed that the power <strong>of</strong> a joint-test <strong>of</strong> linkage and association<br />

was robust to model errors (so long as the analysis model is overly<br />

determined), the test <strong>of</strong> association conditional on linkage can have<br />

difficulty parsing the signal from LD and linkage satisfactorily under<br />

certain analysis options, owing to the nonorthogonality <strong>of</strong> those parameters.<br />

A simulation-based as well as formal analytical description<br />

and explanation will be presented, along with discussions <strong>of</strong> bias-correction<br />

methods to restore the validity <strong>of</strong> this family <strong>of</strong> powerful and<br />

highly sensitive tests.<br />

P08.41<br />

Analytic approaches to power estimation for linkage analysis <strong>of</strong><br />

large pedigrees<br />

G. R. Svischeva, T. Axenovich;<br />

Institute <strong>of</strong> Cytology and <strong>Genetics</strong> <strong>of</strong> Siberian Branch <strong>of</strong> the Russian Academy<br />

<strong>of</strong> Sciences, Novosibirsk, Russian Federation.<br />

The variance-components method is widely used for linkage mapping<br />

<strong>of</strong> quantitative trait loci. Estimation <strong>of</strong> power for this method is<br />

based on asymptotic approximation <strong>of</strong> distribution <strong>of</strong> likelihood ratio<br />

statistics to a non-central chi-squared distribution described by a noncentrality<br />

parameter (NCP). Therefore, evaluating the power can be<br />

reduced to an estimation <strong>of</strong> the NCP. For small pedigrees, the NCP<br />

can be analytically expressed by simple formulas. For large pedigrees,<br />

analytical formulas cannot be deduced because the expectation <strong>of</strong> the<br />

test statistics must be estimated for all possible genotype vectors, the<br />

number <strong>of</strong> whose grows exponentially with increasing pedigree size.<br />

Recently Williams and Blangero (1999) and Rijsdijk et al. (2001) have<br />

suggested ways <strong>of</strong> approximating the NCP by the sum <strong>of</strong> NCP values<br />

for all pairs <strong>of</strong> relatives. Expectation <strong>of</strong> the NCP for any related pair<br />

may be calculated analytically. The effectiveness <strong>of</strong> this approach was<br />

demonstrated for small pedigrees. We have investigated using this approach<br />

for analysis <strong>of</strong> large pedigrees. We have compared two ways<br />

<strong>of</strong> the analytical NCP approximation showing their equivalence, and<br />

investigated the accuracy <strong>of</strong> the analytical NCP estimation for three<br />

large pedigrees and for wide set <strong>of</strong> models <strong>of</strong> quantitative trait inheritance.<br />

We have demonstrated that sample size estimated by the NCP<br />

approximation was slightly overstated (up to 8 %) as compared with<br />

sample size calculated through the exact NCP value. This overestimation<br />

was the same for large and small pedigrees. So, a special correction<br />

could be introduced to obtain unbiased estimation <strong>of</strong> the NCP.<br />

P08.42<br />

Evidence for a susceptibility locus for ménière’s disease on<br />

chromosome 12p12.3.<br />

D. Gabriková 1,2 , J. Klar 1 , C. Frykholm 3 , U. Friberg 3 , S. Lahsaee 1 , M. Entesarian<br />

1 , N. Dahl 1 ;<br />

1 Dept. <strong>of</strong> <strong>Genetics</strong> and Pathology, The Rudbeck Laboratory, Uppsala University,<br />

Uppsala, Sweden, 2 Dept. <strong>of</strong> Biology, Faculty <strong>of</strong> <strong>Human</strong>ities and Natural Sciences,<br />

University <strong>of</strong> Prešov, Prešov, Slovakia, 3 Dept. <strong>of</strong> Surgical Sciences, Uppsala<br />

University, Uppsala, Sweden.<br />

Ménière’s disease (MD) is a disorder <strong>of</strong> the inner ear characterized<br />

by episodes <strong>of</strong> vertigo, tinnitus and fluctuating sensorineural hearing<br />

loss. Most MD cases are sporadic but 5-15% <strong>of</strong> patients are familial<br />

following an autosomal dominant mode <strong>of</strong> inheritance with incomplete<br />

penetrance. The genetic cause <strong>of</strong> the disease remains unknown. We<br />

have previously identified a candidate region for MD on 12p12.3 from<br />

a linkage analysis in three large Swedish pedigrees. Interestingly, affected<br />

individuals <strong>of</strong> two families share a single haplotype within the<br />

linked region, suggesting a possible ancestral mutation.<br />

To further clarify the role <strong>of</strong> chromosome 12p in MD we genotyped 15<br />

Swedish families with familial cases <strong>of</strong> the disease. We analyzed 11<br />

polymorphic marker loci over a 2Mb region in samples from affected<br />

individuals and healthy control subjects. The results revealed association<br />

<strong>of</strong> 5 polymorphic marker alleles to MD (P

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