Background Molecular diagnosis of Huntington’s Disease (HD) can bring challenges sometimes overlooked, as when the molecular diagnosis of a symptomatic person can reveal the pre-symptomatic status of others. We report here how we handled the detection of a homozygous status in a molecular diagnosis that preceded genetic counseling (GC).

Case History Z, a person with motor symptoms since 39 yo, was seen by a neurologist who requested a HTT molecular test and after that a GC with us. Our laboratory detected 44/44 CAG repeats. In light of that, we decided to report that ‘a technical problem had occurred and that a new blood sample should be collected to repeat the test, after consultation’. At our first evaluation, we learned that the patient had consanguineous parents with HD symptoms and three healthy children aged between 18 and 23 yo. All the children were asked to come for follow-up: they were informed that Z had a 33% chance of being homozygous, and that if it was in fact the case, a standard molecular report would simultaneously reveal that all three were obligate carriers. To solve the tangled situation, two choices were proposed: (a) the usual DNA report would be delivered if all children chose to know their own genetic status; or (b) Z report would only mention the final diagnosis without including the HTT genotype. In separate GC sessions, two children decided not to know their genetic status. The family chose (b). A second blood collection was taken, DNA result was the same and reported as (b).

Conclusions The usual procedure for the present molecular diagnosis would disclose unsolicited pre-symptomatic status of all children. The ‘merciful lie’ presented at the first collection allowed the postponement of disclosure and the autonomous decision of these relatives. Cases like this remind health professionals about the importance of analyzing the family history before asking for a definitive genetic test, in order to avoid unwanted predictive diagnosis.