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Old 12-16-2014
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Default germline mosaicism vs variable expressivity

Can someone explain the difference between germline mosaicism and variable expressivity in terms of the following question:

A 15-year-old boy has intracranial neoplasms, mental retardation, and seizures associated with tuberous sclerosis complex, an autosomal dominant disorder. His 41-year-old mother is healthy but has angiofibromas, which are benign skin lesions characteristic of tuberous sclerosis complex. Which of the following best explains the findings in the boy and his mother?

Answer --> variable expressivity
other choice --> parental germline mosaicism

I just want to know how you would tell these two answers apart when coming across a question like this. From my understanding, presence of mosaicism can lead to a decreased severity of a disease, but variable expressivity can as well?

Please clarify for me as thorough as you can. Thank you!
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Old 12-16-2014
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Quote:
Originally Posted by coolguy2 View Post
A 15-year-old boy has intracranial neoplasms, mental retardation, and seizures associated with tuberous sclerosis complex, an autosomal dominant disorder. His 41-year-old mother is healthy but has angiofibromas, which are benign skin lesions characteristic of tuberous sclerosis complex. Which of the following best explains the findings in the boy and his mother?

Answer --> variable expressivity
other choice --> parental germline mosaicism
In germline mosaicism only the germ cells have mutation and the person (Parent in this case) wont have the disease at all but thier kids will. And if you see the somatic cell of these individual (parents), it wont show any mutation. Where as in variable expressivity, Their cells both somatic and germline would show mutation but the phenotype will be less severe or more severe.

The clue which I use while solving this type of question is that, if they say all the kids had the disease but the parents didnt and if the disease was autosomal dominant, then I choose "germline mosaicism".

Hope this helps
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