A 19-year-old male, at a routine physical examination for sports activities (long-distance running) at his college, is noticed to have elevated fasting blood glucose levels (about 7.5 mM). Measurements of C-peptide and insulin levels were close to normal under fasting conditions. After eating, blood glucose levels are only slightly elevated above the normal fasting levels before stabilizing at the fasting levels. The student indicates that he is not drinking or urinating excessively, but that he remembers that his mother had gestational diabetes when pregnant with him. This alteration in glucose homeostasis is best typified by which one of the following types of inheritance?
Correct Answer: Autosomal dominant
Description: The patient is displaying the signs of maturity onset diabetes of the young (MODY), which can be caused by a mutation in the pancreatic glucokinase gene, such that its Km is increased. The increase in the Km for glucokinase would lead to glucose only being metabolized at higher-than-normal levels. Once glucose is metabolized in the b cells of the pancreas, and adenosine triphosphate levels increase, then insulin can be released. The glucokinase mutation causes insulin release to occur at higher-than-normal glucose levels. The mother also expresses the mutant glucokinase gene. During pregnancy, the effect of placental hormones tends to inhibit insulin's action, and in a mother with MODY, in which insulin is not being released appropriately owing to the glucokinase mutation, blood glucose levels rise significantly during the pregnancy, leading to gestational diabetes. MODY, in terms of the glucokinase mutation, is transmitted in an autosomal dominant manner.
Category:
Biochemistry
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