What is the inheritance of thanatophoric dysplasia?
Thanatophoric dysplasia (TD) is considered a dominant disorder, because it is caused by a mutation in only one of the two copies of the FGFR3 gene. (Recessive disorders require the presence of a mutation in both copies of a specific gene to produce the disorder.) Normally, an individual with a dominant disorder has a 50% chance of passing on the disorder to his or her offspring with each pregnancy. However, because TD is almost always lethal in the prenatal or neonatal period, most new cases of TD arise because of a de novo, or "brand new" mutation.
- link url="https://ghr.nlm.nih.gov/condition/thanatophoric-dysplasia#genes"]Thanatophoric Dysplasia - Genetics Home Reference[/link]
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What is the chance of having another baby with thanatophoric dysplasia?
Following the birth of a child with thanatophoric dysplasia (TD), many couples worry about the likelihood of having another affected child. The recurrence risk is thought to be extremely low, given that nearly all cases of TD are due to a de novo mutation. However, there is a very small, theoretical chance that a parent may have two normal copies of the FGFR3 gene in all of his or her cells EXCEPT for the gametes (eggs or sperm). This situation is called "gonadal mosaisicm", referring to the gonads - the organs that produce our eggs or sperm - having a mutation that is not present in the remainder of the parent's cells. If a parent had gonadal mosaicism, it is possible that the couple could have more than one affected child. While gonadal mosaicism has been reported in other disorders, it has never been reported TD. Thus, the most accurate answer for the recurrence risk is that it is likely to be exceedingly low, but is not zero.