In patients affected by ARVC/D, a family history of the disease has been found in 30%-50% of cases, with autosomal dominant transmission in the majority of cases .
Nava et al.  studied 132 subjects belonging to 37 families affected by ARVC/D and classified subjects into three groups according to the RV size and/or wall motion abnormalities observed on echocardiogram:
1. Mild form: a slightly increased (<75 ml/m2) or normal right ventricular end-diastolic volume (RVEDV) with localized hypokinetic or akinetic areas of the RV, in the presence or absence of tra-becular derangements and thickened, hyper-reflective or dense moderator band;
2. Moderate form: RVEDV ranging from 75 to 120 ml/m2 with localized hypokinetic or akinetic and/or dyskinetic areas of the RV in the presence of trabecular derangement and thickened, hyperreflective or dense moderator band;
3. Severe form: RVEDV greater than 120 ml/m2 with widespread akinetic and/or dyskinetic areas of the RV with parietal diastolic bulging.
In this series 64% of family members were found to have a mild form of the disease, 30% a moderate form, and 6% a severe form. Moreover, evaluation of RV wall motion abnormalities demonstrated that the regional dysfunction was more frequent in the infero-posterior wall regardless of the extent of disease. Aki-nesia or hypokinesia of the RV apical region were more common in mild or moderate forms, while in patients with the severe forms, RV wall motion abnormalities of the apical and anterior regions were present in a similar proportion.
Finally, echocardiography in these family members demonstrated that RVOT dilation was related to the disease extent, being present in 100% of severe forms, 50% of moderate, and 29% of mild forms.
The recent identification of several genes whose mutations have been associated with the disease [17-23] offers for the first time the opportunity to study families carrying ARVC/D gene mutations. This allows evaluation of the entire clinical spectrum from concealed to overt forms of the disease. In a study of four families with desmoplakin mutation, echocardiographic abnormalities were found in 14 of 26 mutation carriers (54%), with left ventricular involvement in half of them . Interestingly, subjects with the same mutations could have different clinical presentations, with disease extent ranging from mild to severe forms. Similarly, a recent paper analyzing nine families with plakophilin-2 mutations found that of 32 subjects mutation carriers who underwent clinical evaluation, right ventricular abnormalities on imaging techniques were present in 22 (68%) .
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