Familial dilated cardiomyopathy (DCM) should be an "evidence-based" diagnosis 
derived from clinical and echocardiographic screening of informed and consenting 
relatives of index patients, and on the examination of clinical reports for 
deceased relatives. Most familial dilated cardiomyopathy pedigrees show an 
autosomal pattern of inheritance. Very few of them are X-linked and matrilinear. 
Autosomal recessive inheritance is difficult to be assessed in an evidence-based 
setting. By linkage analysis, several loci, but no disease gene, have been 
identified. At present, few cases of familial dilated cardiomyopathy can benefit 
of a molecular diagnosis. The diagnosis of dystrophin defect-related dilated 
cardiomyopathy is important for patients and families, especially for carrier 
detection. These patients present X-linked inheritance, dominant cardiac 
involvement and raised levels of serum creatine phosphokinase. Defects of the 
glycoprotein complex associated to dystrophin (DAG) are rare skeletal muscle 
diseases with possible cardiac involvement. Mitochondrial diseases, both pure 
cardiomyopathies and multiorgan syndromes involving the heart, are associated to 
defects of mitochondrial DNA genes or of nuclear genes coding for mitochondrial 
proteins. Barth's syndrome develops in male children with granulocytopenia, 
dilated cardiomyopathy, and methylglutaconic aciduria. Cardiomyopathies with 
atrioventricular block are observed in hemochromatosis, Emery-Dreifuss syndrome, 
desmin storage disease, and in isolated familial dilated cardiomyopathy. Actin 
defects were recently identified in 2 unrelated patients with familial dilated 
cardiomyopathy. Desmin defects were also recently identified in 1 familial 
dilated cardiomyopathy. The overall knowledge, although in progression, is still 
limited. Clinical family screening identifies familial forms, preclinical cases, 
and inheritance pattern. By candidate gene screening, the molecular diagnosis 
can be provided for dystrophin, DAG, mitochondrial DNA, actin and desmin gene 
defects.