Even the basic facts of life taught in elementary school and junior high may not apply to all of us. About one in 3500 people, for example, did not get one copy of each chromosome from mom’s egg and half from dad’s sperm. Some of us got both copies of a chromosome from the same parent, said Fox Chase Cancer Center Researcher David Wiest.
In a paper published this week, Wiest described how this situation cropped up in a medical mystery that would have made for a good episode of House. The patient was a six year old boy with a genetic disease known as Severe Combined Immunodeficiency (SCID). Children with this disease start getting stubborn infections soon after about 6 months of age, when they lose protective antibodies that come from their mothers.
A number of different genetic mutations can cause the problem by preventing the body from making crucial parts of the immune system – B cells and T cells.
Weist is collaborating with Duke University researchers, examining the genetic mutations responsible for the disease. In most cases, people inherit a faulty gene from each parent. In a few others, the faulty gene is on the X chromosome, and in those cases boys will get the disease but not girls, since girls have a second X as a backup.
But in this particular boy, it appeared he got the disease a different way – the faulty gene was on chromosome 1, but only his mother carried the mutation. His father’s chromosome 1 was normal. That was baffling, said Wiest. Sometimes such cases crop up for a mundane reason – that someone else is the biological father (Just the kind of plot twist that makes for good medical dramas).