Medical Genetics The most common kinds of defect are those affecting the limbs (arms and legs). These include missing or extra fingers or toes deficiencies in limb length and abnormalities in positioning, such as club footMedical Genetics The most common kinds of defect are those affecting the limbs (arms and legs). These include missing or extra fingers or toes, deficiencies in limb length, and abnormalities in positioning, such as club foot