A study of a large number of twins suggests that ADHD behaviors exhibit a notable degree of heritability, with 11% of the variation in children's ADHD behaviors attributed to shared genetic factors between generations. The study indicates that children tend to resemble their parents in levels of impulsiveness, hyperactivity, and inattention due to shared genetic influences rather than shared home environments or effects of parental ADHD on child ADHD. While genetic factors play a significant role, the main cause of ADHD is likely an interplay of unique environmental factors for each child.
A Swedish study found that the risk of developing multiple sclerosis (MS) is similar between first- and second-degree family members of people with relapsing-remitting MS (RRMS) and primary progressive MS (PPMS). The study suggests that genetics and environment contribute equally to disease risk and that the likelihood of developing a particular MS type may be independent of genetics. The heritability of MS overall was estimated to be about 51%, with RRMS having a heritability of 55%. The study highlights the need for further research to explore other genetic and environmental risk factors that contribute to disease expression.
