Some years ago, a woman in her late 30s was referred to me for consideration for an amniocentesis on the basis of advanced maternal age. She had had three previous pregnancies, all resulting in healthy babies.

An ultrasound confirmed a single, viable intrauterine pregnancy, and a fetal size consistent with dates. The amniocentesis was performed without complications. However, the results of the chromosome culture showed there was a balanced 2 on 17 translocation (Box). This was of concern to me — if this was a new mutation, there would be a significant risk that the fetus could have a neurological disorder, ranging from mild cerebral dysfunction, through to severe intellectual disability. However, most cases that I see with a translocation are not new mutations; they are a reflection of the chromosome makeup of one of the parents.

I contacted the patient, and told her of the result, and requested that her blood and her husband’s blood be analysed for evidence of a translocation. After 72 hours, the laboratory issued the report showing that neither the patient nor her husband had the translocation.

This did alarm me, but when I told the patient about the results, she asked whether it would be reasonable for her boyfriend to have chromosome analysis done as well. I assured her that this would be very useful, and contacted her boyfriend. He supplied blood and, sure enough, it showed that he had a balanced 2 on 17 translocation. I explained to the patient that, under these circumstances, the fetus was very unlikely to have an intellectual disability, and she seemed quite relaxed about this information.

I discussed the result further with the patient’s boyfriend, pointing out to him that it may be possible that his siblings could also have a balanced translocation. If he or his siblings had any further children, these children could be affected. The patient’s boyfriend told me categorically that he was not going to be having any more children. He had a sister who had three children, and she was not going to have any further pregnancies. Nevertheless, his sister agreed to have a chromosome analysis done, which confirmed that she had a normal chromosome complement.

The boyfriend also told me that he had a brother who lived on a farm. When I asked if it was likely that he would have children, he said that his brother was 28 years old and had been damaged by obstetric forceps during a difficult delivery, leaving him with an intellectual disability. This brother agreed to have chromosome analysis, and surprise, surprise, it showed that he had an unbalanced translocation. This then would explain his intellectual disability. I doubt very much whether the obstetric forceps played any role in his condition.

When my patient’s baby was born, a physical examination showed that the baby was normal.

I recount this history to reinforce that sometimes the obvious is not as clear cut as one may first think. The country general practitioner who delivered the boyfriend’s brother 28 years ago has probably laboured under the weight of blame being ascribed to him for the poor outcome in this young man.