Ethical issues in genomic diagnosis and cascade testing

A 6-year-old girl is referred to the genetics clinic. Her father, aged 34, was recently diagnosed with Huntington disease after the onset of chorea and cognitive change. The paternal grandmother died by suicide at 52 and is presumed to have had the condition. The father has three adult siblings, two of whom have not been tested. The parents now ask that their daughter be tested "so we can plan her future and know what we are dealing with." The girl is well, developing normally, and is unaware of the family diagnosis. **(a)** What is the internationally agreed ethical position on predictive genetic testing of a child for an adult-onset condition, and what principle underpins it? *(4 marks)* **(b)** Outline the pre-test counselling conversation you would have with the parents, and explain why testing their daughter now would not be offered. *(6 marks)* **(c)** The family later undergoes trio exome sequencing for an unrelated indication in the daughter, and a medically actionable secondary finding is reported in a hereditary cancer gene. The family cannot recall being asked about secondary findings. How should this situation be managed, and what does it reveal about the consent pathway? *(5 marks)* **(d)** A pathogenic variant is later confirmed in the daughter for an unrelated, childhood-actionable condition. Outline your approach to cascade testing of the at-risk relatives, including the role of the proband's consent and the relatives' right not to know. *(5 marks)*