Twinstudy

Twin study at Helsinki University in English

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The Family Study of Nicotine Dependence

It is known that some smokers acquire dependence to nicotine more quickly and strongly. It has been found that the individual differences in the development of nicotine dependence are due to both genetic and environmental factors. Aim of the project is to provide new knowledge of the genetic basis of smoking behaviour including phenotypes such as nicotine dependence, nicotine withdrawal and smoking cessation, for example. Understanding environmental influences and health-related effects of smoking are also of interest to the group.

Ongoing genotyping projects in different datasets

Nicotine addiction genetics (NAG, e.g. family study of nicotine dependence)

This family sample is a subsample of a larger twin cohort study. The original sample of twins Finland born in Finland between 1938 and 1957 was collected in 1975-1997 by Jaakko Kaprio and Markku Koskenvuo. In 2001-2006, the twin pairs concordant for smoking were contacted again and phenotyped extensively for smoking-related traits. In addition, family members of the twin pairs were included. These consist mostly of siblings as at the time of the data collection most of the twins were relatively old and thus no parents were available for the data collection. Altogether, the family study sample consists of 2265 individuals belonging to 762 families.

Linkage study

Altogether 550 family members (from 153 families) from the family sample were selected to the genomewide scan with 380 microsatellite markers. The data from this scan has been used in several articles, mostly combined with Australian data collected with similar design. The articles and their main results are presented below:

Based on these results, selected markers have been chosen for genotyping in an additional sample of the Finnish family data consisting of 800 individuals belonging to 211 families. A total of 19 markers residing on chromosomes 5, 7, 10, and 11 have been successfully genotyped. The combined data of the original and additional data set is currently being analysed using non-parametric linkage analysis.

A fine-mapping of the chromosome 20 region in the combined scan and replication sample and replication of linkage results on chromosome 22 are underway. This "additional" or "replication" sample includes 786 individuals (206 families) belonging to families with three of more siblings participating in the study.

Candidate gene study

Altogether 144 SNPs residing in dopamine receptor (DRD1, DRD2, DRD3, DRD4, DRD5,), nicotine receptor (CHRNA3, CHRNA4, CHRNA5, CHRNA7, CHRNA10, CHRNB2, CHRNB4) and other relevant (CNR1, PTEN) genes have been genotyped in 642 NAG individuals (selected based on concordance for heavy smoking) and 675 FinnTwin16 individuals.

The association analyses of the data are underway.

GWA

The original twin pair (index pair) samples of the family study have been sent to the Wellcome Trust Sanger Institute in March 2009 together with other twin (older Cohort & FinnTwin16 samples (based on discordance for obesity, alcohol use, smoking, long-term physical activity and hormone replace therapy) . These, altogether 1448 samples will be genotyped with GWA-CNV Illumina 670K chip.

Health2000 & ATBC (NIH grant project)

The aim of this project is to further study the Chr22 region identified in the genome-wide scan. In the first phase, around 1000 case (ATBC, men who smoke >40 cigarettes/day) and around 1000 control (Health1000, men representing the population) samples will be sent to CIDR for genotyping. The DNA of the ATBC samples has still to be extracted. Two students have been recruited for that task. They started their job in February 2009 and the aim is to extract the DNA of the majority of the phase I ATBC samples before April 2009.

The phase two genotyping, including around 2000 cases (ATBC, men smoking 30-39 cigarettes/day) and around 2000 controls (Health2000, men representing the population), will be performed in the Finnish Genome Centre. Only the SNPs with the most significant or otherwise interesting results will be genotyped in the phase II.

FINRISK

A population-based FINRISK 2007 data, collected in National Institute for Health and Welfare (THL), Helsinki, includes 1750 adults in the smoking sub-sample. THL has a long history of collecting population based cardiovascular risk factors health surveys at five year-intervals since 1972. For the first time in year 2007 there was included a very detailed smoking related questionnaires including multiple nicotine dependence scales (FTND, NDSS, HONC) and detailed information of smoking status; this belongs to the SOKRAS subsample, from which 600 persons residing in Helsinki have been selected for GWAs and gene expression studies. Cotinine & 3-hydroxy-cotinine determinations from serum samples have been carried out and it is possible to compare measures of smoking behavior and nicotine dependence. Genotyping of some blood samples of these data are under way. Multidisciplinary methodology from epidemiology, genetics, statistics, and behavioral sciences will be used for analyses.

FinnTwin16

FinnTwin16 is longitudinal study of five consecutive birth cohorts (1975-1979) of Finnish twins, their sibling and parents. The study was initiated in 1991 as the twins were 16 years old (baseline) and included a questionnaire assessments with detailed smoking data. Similar assessments were conducted again at age 17, 18½, and at young adulthood (ages 22-25). With response rate exceeding 88%, data is available from over 2500 extended families.

FinnTwin16 data has been used in examination of nicotine addiction genetics together with NAG sample both in the candidate gene study and in GWA study (see above).

Today & future in the project

At the moment, the main efforts at the project concentrate on analysing the linkage replication results for the data already available (Chr 5, 7, 10, 11) and organizing genotyping for two additional chromosomes (Chr20 & 22) in the family data. In addition, the final data from the candidate gene SNP genotyping has been recently received and the QC of the data is underway. Thus, very soon this data will be analyzed and also combined to the microsatellite data on the overlapping regions. Finally the GWAs data will become available for analyses of much more detailed smoking and ND phenotypes than available in most other studies with GWAs data (Genomeutwin; Vink et al, Am J Hum Genet 2009; ENGAGE, TAG, WTCCC/GSK; GENEVA).

Within the year 2009, the phase I samples of the NIH project (ATBC & Health2000) will be genotyped and the data will be analyzed. These results will determine the SNPs genotyped and genes investigated further in the project (phase II).

The project group staff in Finland

P.I. Professor Jaakko Kaprio
Professor Leena Peltonen
Senior Scientist (Geneticist) Anu Loukola
Post-doctoral researchers Ulla Broms and Kaisu Keskitalo
MSc students (lab technicians) Maija Järvinen and Jenni Wickholm
Statistician Janne Pitkäniemi
Supervisor, Head of Interviewers Anja Häppölä
Systems Specialist Kauko Heikkilä
Senior Scientist Outi Salminen
Senior Scientist Tellervo Korhonen
PhD students Maria Hukkinen, Marine Largeau, Emma Nyman and Juho Wedenoja

Finnish group works in a close collaboration with the group of Dr. Pamela Madden (Washington University, St. Louis, MO, USA) and Prof. Nicholas Martin (Queensland Institute of Medical Research, Queensland, Australia). Madden is the P.I. of the NIH project and Martin's groups has collected data on Australian twins using similar study design as the Finnish NAG study.

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