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Old 01-23-2014
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Question Genetics Question PLEASE someone explain

I GOT a question that went like this:

5 YEAR OLD BOY COMES CAUSE OF YELLOW DEPOSITS IN HIS EYELIDS, BOTH PARENTS HAVE A HISTORY OF HYPERCHOLESTEROLEMIA (BOTH 300-400MG/DL) SINCE CHILDHOOD.
THE BOYS LIPID PROFILE SHOWS 850MG/DL OF TOTAL CHOLESTEROL.
IF PATIENT GROWS UP AND HAS A CHILD WHAT ARE THE CHANCES OF HIS CHILD TO HAVE HIS DZ?

A) 0
B) 1 IN 4
c) 1 IN 2
D) 3 IN 4
E) 1 IN 1

answer was E. could someone kindly explain why is this?
the dz is autosomal dominant and its supposed to be 1 in 2 chances (50%) of having a child with the same disease, why is 1 in 1? if its due to its HOMOZYGOUS mutation, does this apply to ALL AUTOSOMAL DOMINANT MUTATIONS?
that when they are homozygous for an autosomal dominant dz they will have the 100% chance of having a kid with the same dz?
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Old 01-23-2014
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Quote:
Originally Posted by drpisho View Post
I GOT a question that went like this:

5 YEAR OLD BOY COMES CAUSE OF YELLOW DEPOSITS IN HIS EYELIDS, BOTH PARENTS HAVE A HISTORY OF HYPERCHOLESTEROLEMIA (BOTH 300-400MG/DL) SINCE CHILDHOOD.
THE BOYS LIPID PROFILE SHOWS 850MG/DL OF TOTAL CHOLESTEROL.
IF PATIENT GROWS UP AND HAS A CHILD WHAT ARE THE CHANCES OF HIS CHILD TO HAVE HIS DZ?

A) 0
B) 1 IN 4
c) 1 IN 2
D) 3 IN 4
E) 1 IN 1

answer was E. could someone kindly explain why is this?
the dz is autosomal dominant and its supposed to be 1 in 2 chances (50%) of having a child with the same disease, why is 1 in 1? if its due to its HOMOZYGOUS mutation, does this apply to ALL AUTOSOMAL DOMINANT MUTATIONS?
that when they are homozygous for an autosomal dominant dz they will have the 100% chance of having a kid with the same dz?
Yes homozygous for an autosomal dominant disease = 100% chance offspring will be affected. This is very rare as most autosomal dominant diseases cause death before birth or very early if homozygous.

Type 2 dyslipidemia - familial hypercholesterolemia (the disease in this question) causes disease in a heterozygote and severe disease in a homozygote. As this boy has severe hypercholesterolemia at a young age, and both his parents have hypercholesterolemia, its likely he is homozygous for this autosomal dominant disease, so there is a 100% chance that he will pass the disease on to all his offspring.
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drpisho (01-23-2014), wa87el (01-23-2014)
  #3  
Old 01-23-2014
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awesome usmleuk!!!
thank you
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