Familial Trends in Left Handedness

Handedness is regarded as continuum ranging from strong right handedness across mixed handedness to strong left handedness. Left handedness affects only 8-15% of the human population, and the exact cause is unknown. Therefore, the present study was planned on left-handed subjects with the aim to trace the familial correlation of their handedness to find out genetic basis, if any, for left handedness. Present study is a trace back study which was conducted on 30 left-handed subjects (primary Subjects) and their family members (secondary subjects).

Handedness was evaluated based on criteria suggested by Raczkowski. Frank Left handedness was found to be running among 50% (15/30) of the families. In 16.7% families left handedness could be traced back to 2-3 more generations. In familial distribution, left, ambidextrous or forced right handedness was more prevalent in mothers (p = 0.05). Inheritance is more prevalent in families with affected mother as well as father.

The conclusion is that left-handedness has a strong hereditary correlation and that inheritance is more common in families with left-handed parents. It also correlates with maternal left handedness, and while inheritance is X-linked, the pattern of inheritance is autosomal.