In some genetic counseling textbooks, it is mentioned that in DMD/BMD cases there is 15-20% chance that the mother is germline mosaic (so no pathogenic variant is found in peripheral blood genetic testing) and can pass the pathogenic variant to more than one child. I am wondering if this phenomenon is specific to DMD/BMD since germline mosaicism is usually a rare situation in genetic counseling/clinical genetics.
Andy L.C Hui Germline mosaicism is commonly seen for X-linked disorders, and can account for recurrence of the disease like DMD or hemophilia though the mother is apparently not a carrier on blood testing. We do MLPA testing for identifying carrier status in maternal blood. This can detect the deletion or duplication which has been earlier identified in previous child or close relative. This maybe negative, still the female may have another affected child. Suppose the mother has two affected male children earlier or one affected male child and her brother affected earlier, then she would be an obligate carrier.
Inusha is right; you will find nearly in all X-linked diseases germline mosaicism, like Fabry's disease, Danon's disease and even in Fragile X Disease. There is one exception and this is Hunter's syndrom (MPS II). Why it is not clear.
Best
Chris
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