All disorders genetc. Only some are chromasomal.
See below. Homocystinuria is a genetic disorder which affects the metabolism of the aminoacid methionine. It is inherited as a autosomal recessive trait trait, ie the child must inherit the non working gene from both the parents to be affected. It presents as failure to thrive, mental retardation, visual problems and bone problems.
Tend to run families.. ..But no association I am aware of w/any genetic problems.