Familial idiopathic scoliosis is the type of curvature of the spine that runs in families and has no known cause (idiopathic). While both boys and girls are pretty well equal in number with the mild curves in the spine, the girls begin to outnumber the boys significantly with the moderate to severe curves.
It isn’t understood why girls are affected more than boys, but boys can develop moderate to severe scoliosis and may also require bracing or surgery, just as the girls may.