Moreover, considering our preliminary observations that a) the severity of cardiomyopathy may tremendously differ between (unrelated) MD patients of the same age having exactly the same dystrophin gene deletion and b) a similar severity of cardiac disease is frequently detected in MD siblings of similar age (suffering from the same dystrophin gene mutation), the presence of additional genetic modifiers that determine cardiac disease severity is highly expected. This evidence concerns the gene DMD and Menkes disease.