Nearly 80 per cent of schizophrenia risk may be traced back to genes inherited from the child's parents, according to the largest study of twins for the disorder to date.
"The new estimate of heritability of schizophrenia, 79 per cent, is very close to the high end of prior estimates of its heritability," researchers said, referring to previous estimates that have varied between 50 and 80 per cent.
Researchers, including those from the University of Copenhagen, used a record of all twins born in Denmark since 1870 to assess genetic liability in over 30,000 pairs of twins.
They found a similar estimate of 73 per cent, indicating the importance of genetic factors across the full illness spectrum.
"This study is now the most comprehensive and thorough estimate of the heritability of schizophrenia and its diagnostic diversity," said Hilker.
"It is interesting since it indicates that the genetic risk for disease seems to be of almost equal importance across the spectrum of schizophrenia," even though the clinical presentation may range from severe symptoms with lifelong disability to more subtle and transient symptoms, said Hilker.
"Hence, genetic risk seems not restricted to a narrow illness definition, but instead includes a broader diagnostic profile," she said.
The researchers used a new statistical approach to address one of the factors that contributes to inconsistencies across previous studies.
Usually studies of heritability require that people be classified as either having schizophrenia or not, but some people at risk could still develop the disease after the study ends.
Researchers applied a new method to take this problem into account, making the current estimates likely the most accurate to date.