Epidemiology
Cell division errors can be due to a lack of nutrients or availability of atomic building blocks, or the presence of toxins that impede normal growth. Division errors which occur very early in the development of a multicellular organism can result in large scale structural and functional differences in the organism's final shape. For example it is now understood that a lack of folic acid in the diet of a mother can cause cellular neural tube deformities that result in Spina Bifida.
External physical shocks or constrainment due to growth in a restricted space, may result in unintended deformation or separation of cellular structures resulting in an abnormal final shape or damaged structures unable to function as expected.
For multicellular organisms that develop in a womb, the physical interference or presence of other similarly developing organisms such as twins can result in the two cellular masses being integrated into a larger whole, with the combined cells attempting to continue to develop in a matter that satisfies the intended growth patterns of both cell masses. The two cellular masses can compete with each other, and may either duplicate or merge various structures. This results in conditions such as conjoined twins, and the resulting merged organism may die at birth when it must leave the life-sustaining environment of the womb and must attempt to sustain its biological processes independently.
Read more about this topic: Congenital Disorder