Bipolar Disorder Autosomal Trait

Bipolar disorder (or manic depression) is characterized by excessive mood swings. These swings range from highs (mania) to lows (depression). While the exact cause of bipolar disorder is unknown, it seams to run in families, handed down from one generation to the next. The reason for this is genetic. Autosomes, a form of gene that is neither male nor female, passes the bipolar disorder from parent to offspring.

Twin Studies

• Twin studies support that bipolar disorder is transmitted through an autosomal trait. Fraternal twins show a strong genetic component in bipolar disorder. Identical twins share all their genes, while fraternal twins share about half. Because identical twins are more likely to both have bipolar than fraternal twins, the genetic element is stronger than the nurture factor. So passing on bipolar disorder through the autosomal trait is likely.

Adoption Studies

• Adoption studies allow researchers to examine which parent the adoptee will favor. If an autosomal trait is present, the adoptee will be like the birth parent. Subsequently, if the adoptee is like the adoptive parent, no autosomal trait is present. Findings show adopted adults are more likely to have bipolar disorder if their biological parent had it. Thus examinations of adoptive adults support the autosomal trait.

Family Studies

• Family studies permit the study of an autosomal trait. Children of a bipolar parent are at risk of inheriting bipolar disorder. Likewise, siblings were found to have an increased chance of inheriting bipolar disorder if they had a sibling with the condition. Half siblings with the same mother were also at risk of having bipolar disorder. The same was true for half siblings with the same father. These findings support the transmission of bipolar disorder through genetic means.

Linkage Studies

• Because bipolar disorder has several variations, it is known as the "bipolar spectrum." In linkage study by Elaine Green, Ph.D. et al, the spectrum was limited to Bipolar I and Bipolar II. This helped to narrow the definition of bipolar. Their study supported the passing of Bipolar I or II through the autosomal trait. They interpreted their data to be consistent with this narrow definition of bipolar.

Conclusion

• While the exact gene or genes have not been identified as the carrier for bipolar disorder, other analyses give support to the autosomal trait. Twin studies yielded a positive relationship between genetic similarity and heritability of bipolar. In adoptive studies, children with bipolar birth parents inherited the disorder. When studying families, both children and siblings and half siblings were found to inherit the condition more than the general population. Linkage studies have found an autosomal trait to be present in their investigation.