Ten month later, the parents came again to the consultation. Cardiac examination, including echocardiography and ECG, was normal within the family. A heterozygous mutation was found in the cardiac troponin T gene (R141W mutation) in the deceased infant (blood sample was performed before death). The consequences of this genetic result were discussed with the parents. In the same time and consultation, the mother indicated that in fact she was pregnant again (three months). The parents asked for the mean to prevent the transmission of the disease, including the possibility to perform prenatal diagnosis through amniocentesis, and to discuss medical abortion if the foetus would carry the mutation.
At the first cardiogenetic consultation, the possibility of a genetic and mendelian origin of the Dilated Cardiomyopathy of the infant was discussed. Several reports indicate that DCM is monogenic in about 20 to 45% of cases, supporting the principle of a systematic cardiac examination in first degree relatives, whatever the familial context and history. In the present case, and reinforced by the severity and precocity of DCM, cardiac examination was recommended in the parents and the other child. Clinical examination, ECG and echocardiography were normal. It was told to the parents that the risk of another child with DCM was low, but not zero, due to the possibility of incomplete penetrance, or de novo mutation or recessive inheritance.
At the second cardiogenetic consultation, ten months later, genetic result was in favour of an autosomal dominant inheritance and interestingly the same mutation was previously described with this mode of inheritance in another DCM family. The risk for a future child was therefore 50%. Prenatal diagnosis was extensively discussed with the parents through a multidisciplinary team including a cardiologist, a geneticist, a psychologist and an obstetrician. The severity of the mutation was also observed in the previous family/report.
A consensual attitude was to accept prenatal diagnosis if still requested by the parents. Genetic status was determined in the same time in the parents. Surprisingly the two parents did not carry the mutation (and the other child did not). After internal laboratory checking for right paternity, it was conclude that the mutation of the infant was a de novo mutation (neomutation that occurred in the infant for the first time in the family, the mutation usually concerning one germinal cell of one of the parents). There was therefore no risk of transmission for a future child and the parents were reassured. A rare hypothesis was however discussed, the possibility of recurrence of DCM due to the presence of the mutation in several germinal cells of one of the parents (a mechanism known as germline mosaicism). The very low probability of this hypothesis led us to consider prenatal diagnosis as not mandatory and it was not requested by the parents. Six months later, the newborn was healthy.
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