There are a couple of things I didn’t explain very well in my previous post about the strange case of the 13-year-old girl suing a sperm bank using product liability law, on the grounds that the sperm used to conceive her carried a genetic defect resulting in her mental retardation.
First and foremost, what’s with a girl inheriting Fragile X Syndrome from her father? This syndrome is (as you might expect) caused by mutations in a region located on the X chromosome, and the classic pattern of inheritance of X-linked diseases is that males are affected while females are “carriers” (who may also be affected, but usually much less severely) who can then pass the condition on to their own sons. Under this scenario the girl’s story makes no sense: it seems implausible that a man with frank Fragile X Syndrome would be accepted as a sperm donor, and the girl herself should display much milder symptoms than her father.
However, the inheritance of Fragile X is more complex than the typical X-linked disorder due to the wonders of repeat expansion, which can cause the mutation to vary in severity from generation to generation. Female carriers of a severe FX mutation can indeed be cognitively affected, and some males with the mutation show a relatively mild form of the disease. Although it appears to be rare for a mildly affected male to produce a more severely affected daughter, there is at least one prior reported case of a girl affected by Fragile X inherited from a sperm donor (the linked study is in fact what triggered the girl’s mother to pursue this case).
Secondly, why is the girl bringing the case forward rather than the mother? The answer appears to be that the mother tried, but failed due to the statute of limitations – a problem that doesn’t apply to the daughter:
[Judge] O’Neill, however, dismissed all claims brought by her mother, Donna
Donovan, after finding that the statute of limitations had long expired
because the test done over a decade ago showed that the sperm donor was
the source of the Fragile X genetic defect in her daughter. Brittany
Donovan’s claims, however, are still viable, O’Neill found, because the
Pennsylvania Minors Tolling Statute provides that the clock does not
begin to run until two years after the minor reaches the age of 18.
Anyone interested in the gory details of the case can read the judge’s complete 23-page verdict here.