Problem: A 49 year old man has been referred for evaluation and management of re

Question

Problem: A 49 year old man has been referred for evaluation and management of recently diagnosed diabetes mellitus. His parents did not have diabetes. Both of his brothers (aged 52 and 55) also have diabetes. They have 2 sisters aged 44 and 45 who are unaffected. He is worried for the future of his sons aged 23 and 27.

Answer?
1. Diabetes mellitus is related almost exclusively to environmental factors and genetic factors are not significant

2. The pattern of disease in this family means that his sisters have probability of close to 100% of developing diabetes mellitus later in life

3. If analysis shows that all 3 have the same paternal Chromosome 17 homolog and both daughters share the other paternal Chromosome 17 homolog - this is likely to be a chance finding

4. The brothers are likely to have inherited a specific abnormal variant of the Maturity Onset Diabetes Mellitus allele on the long arm of chromosome from both parents.

5. If linkage studies show all 3 brothers have inherited the same homolog of Chromosome 17 from their mother this suggests that the condition is linked to a defect on Chromosome 17

Explanation / Answer

5. If linkage studies show all 3 brothers have inherited the same homolog of Chromosome 17 from their mother this suggests that the condition is linked to a defect on Chromosome 17.

Maturity Onset Diabetes Mellitus is associated with abnormality in chromosome 17 and inherited in an autosomal dominant fashion (means, can be inherited from either mother or father) with 40% to 90% penetrance. In this case, the sons inherited defective allele from their parents, but the parents are not affected may be because of low penetrance.

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