Projects based on twin data

At present, about 30 ongoing projects based on the Twin Registry cover a broad spectrum in public health. Some areas being investigated are aging, dementia, allergy, cancer, and cardiovascular diseases.

Other projects focus on effects of gender differences on health and life situations. We have collected data on family relationships, including parent-child, marital and siblings, on adult and child mental health, and the individual attributes of family members. Twin parents, their partner and the target child have participated through questionnaires and an interview, using a multi-agent, multi-method strategy.
We collaborate with molecular geneticists who are working on identifying genes that cause different diseases. This mainly refers to cardiovascular and affective disorders. In a study on Parkinson's disease, we assess the importance of environmental factors for the disease in a population-based sample of Swedish twins. There are about 400 twin pairs in this study.

Why is it important to participate in a study?

Taking part in a scientific study may not have direct benefit to the person involved. However, the results of the research have relevance for other people, both in our generation and future generations, who face various forms of diseases. The more people involved, the easier it is for us scientists to arrive at a useful result. Our research will increase the understanding of the causes of diseases which will hopefully be used to prevent and improve treatment in various areas in the future.

It should however be emphasized that it is always optional to participate in studies.

How we work

The Swedish Twin Registry, with information on approximately 97 000 pairs of twins born since 1886 , is the world's largest population-based twin register and is therefore an invaluable resource for the studies of health and health related behaviors. The research method used in twin studies based on the identical twins that have the same genes, while fraternal twins share about 50% of the same genes. When analyzing the survey responses and DNA , and if we find that siblings in a pair of identical twins more often suffer from illness than siblings from a pair of fraternal twins, we conclude that this is caused by heredity. From this result we can proceed to try to find the exact gene that affects the disease progression and which function it has.

How are the answers used and what happens to the results?

All participant responses are aggregated and become statistics. Researchers at Karolinska Institutet analyze the results. Results from the study will be used by physicians and as a basis for future research.

The research results are eventually published in international medical journals.

Ongoing projects

CATSS - The Child and Adolescent Twin Study in Sweden

The aim of the CATSS study is to investigate how both genetic and environmental effects influence health and behavior in children and adolescents.

We initiated the ongoing CATSS study in 2004. In CATSS-9, we conduct a telephone interview with parents of all 1,400 twin pairs born in Sweden annually in connection with their 9th birthdays. By January 2020 we have performed 16,826 interviews with a high response rate (≈70%), and we have collected DNA from the twins (current N≈17,882 individuals). We follow these families with questionnaires to parents and twins at age 15 (CATSS-15; current N=15,470), 18 (CATSS-18; current N=13,092 twins) and 24 (CATSS-24; current N= 4,842 twins)

CATSS is very large and thus has power to study rare conditions and identify subgroups of twins for follow up studies. Since we have information from 16 age cohorts assessed with the same measure we can here investigate how mental health problems among children have changed over time. There are two completed high-risk clinical study (at age 9; CATSS-clinical and at age 15; CATSS-DOGSS 227) and three completed phenotypic studies (asthma, OCD [obsessive compulsive disorder/hoarding]; eye-tracking), as well as 3 ongoing (CATSS-RATSS [ASD]; eating disorders, synesthesia). The main aim is to understand health service inequalities, and to identify factors that predict contact with child and adolescent psychiatry services. The links to our ongoing studies are found on the Swedish page.

Using the CATSS data we have shown that the heritability for ASD was around 80% and that ASD had a common genetic etiology with other neuropsychiatric disorders, that extreme values of ASD and ADHD have the same genetic etiology as normal variation in the underlying traits, and an association between fetal growth on ASD suggesting that fetal growth is in the causal pathway. 

CATSS is a part of several international projects where data from different countries is used to reach better and more convincing conclusions. This gives us the opportunity to compare how things are alike but also different in different countries.

Older projects

Twin Study of Child and Adolescent Development - TCHAD

In the longitudinal Swedish Twin study of Child and Adolescent Development (TCHAD) we have followed 1,500 twin pairs from age 8 to age 26. For example, we have studied how genetic and environmental effects contribute to the development of mental health problems over time. The data include a broad spectrum of measures of environments as well as internalizing and externalizing problems behaviors from both twins and parents. The study is designed to address the interplay between genes and environments, comorbidity, and the development into adult psychopathology. We will continue our studies of antisocial behavior, ADHD, eating problems, fears and phobias, and relationships.

YATSS - A twin study of health and behavior in young adults - Twins born from 1985 to 1992

The purpose of the study is to show how genetic and environment influences diseases. Most common diseases will be studied such as gastrointestinal disorders, pulmonary disease, asthma / allergy , arthritis, affective disorders and symptoms, eating disorders , fibromyalgia, chronic fatigue syndrome and women's health.

PETSS - The PrEschool Twin Study in Sweden - 5 year old twins

The overall aim of the first ongoing project is to investigate both general and specific etiologic processes in childhood ADHD and comorbid conditions (Nigg, 2003) by combining neuroscience and genetic methodologies in a large population-based sample of preschool twins. We will perform a twin study of all 1,400 pairs of 5 year-old twins born in Sweden during 2003.

TOSS - Twin Offspring Study in Sweden

The mail focus of this study is to examine if patterns of genetic and environmental influences on associations between family relationships and women's adjustment also hold for men.Studies that have examined genetic and environmental contributions to measures of family relationships and to associations between family relationships and mental health have found two different patterns of results for adults and children. For children, genetic factors explain most of the covariance between parent-child relationships and child adjustment, while in adults nonshared environmental factors account for most of the covariance between marital relationships and adult adjustment. These different patterns of findings suggest that different mechanisms are involved in linking pertinent family relationships to adjustment in children and adults.

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