CDE Pathophysiology 5 — Questions and Answers
Question 1: Maturity-onset diabetes of the young (MODY) is characterized by which distinctive genetic feature?
- Polygenic susceptibility similar to type 2 diabetes but earlier onset
- Autosomal dominant single-gene mutations impairing beta-cell function (Correct answer)
- X-linked recessive mutations affecting insulin receptor structure
- Mitochondrial DNA mutations inherited only from the mother
Correct answer: Autosomal dominant single-gene mutations impairing beta-cell function
MODY is caused by autosomal dominant mutations in single genes (e.g., HNF-1alpha, glucokinase, HNF-4alpha) that impair beta-cell development or function, distinguishing it from polygenic type 2 diabetes.
Question 2: In gestational diabetes mellitus (GDM), placental hormones contribute to insulin resistance primarily through which mechanism?
- Direct binding to insulin receptors blocking insulin access
- Placental lactogen and progesterone impairing post-receptor insulin signaling (Correct answer)
- Increased fetal glucose consumption requiring maternal glucose output
- Placental insulinase degrading circulating maternal insulin
Correct answer: Placental lactogen and progesterone impairing post-receptor insulin signaling
Human placental lactogen, progesterone, and cortisol secreted by the placenta antagonize insulin signaling at the post-receptor level, creating physiologic insulin resistance that unmasks GDM in susceptible women.
Question 3: Diabetic autonomic neuropathy affecting the cardiovascular system most characteristically presents as:
- Hypertension from sympathetic hyperactivation of the heart
- Resting tachycardia followed by fixed heart rate unresponsive to maneuvers (Correct answer)
- Episodic bradycardia requiring pacemaker implantation
- Exaggerated heart rate response to Valsalva maneuver
Correct answer: Resting tachycardia followed by fixed heart rate unresponsive to maneuvers
Cardiovascular autonomic neuropathy initially causes resting tachycardia from vagal denervation, then progresses to a fixed heart rate as both parasympathetic and sympathetic cardiac innervation is lost.
Question 4: Which of the following correctly describes the pathophysiology of hypoglycemia unawareness in diabetes?
- Peripheral glucose sensors stop detecting low blood glucose
- Recurrent hypoglycemia shifts the glycemic threshold for counterregulatory responses to lower glucose levels (Correct answer)
- Beta cells begin secreting insulin at lower glucose concentrations over time
- The brain adapts to use ketones instead of glucose, masking symptoms
Correct answer: Recurrent hypoglycemia shifts the glycemic threshold for counterregulatory responses to lower glucose levels
Recurrent hypoglycemia causes both the threshold for counterregulatory hormone release and the threshold for symptom perception to shift to lower glucose values, reducing or eliminating warning symptoms.
Question 5: Secondary diabetes mellitus caused by chronic pancreatitis differs from type 1 and type 2 in that it features:
- Higher rates of macrovascular complications due to inflammation
- Impaired glucagon secretion from alpha-cell damage making hypoglycemia more severe (Correct answer)
- Absolute insulin deficiency with intact counterregulation like type 1
- Predominantly hepatic insulin resistance without beta-cell loss
Correct answer: Impaired glucagon secretion from alpha-cell damage making hypoglycemia more severe
In pancreatogenic (type 3c) diabetes, destruction of both alpha and beta cells means glucagon secretion is also impaired, resulting in labile glucose control and increased severe hypoglycemia risk without glucagon rescue.
Question 6: The hexosamine biosynthesis pathway contributes to diabetic complications by:
- Directly glycating extracellular matrix proteins in basement membranes
- O-GlcNAc modification of transcription factors altering gene expression and causing endothelial dysfunction (Correct answer)
- Competing with glycolysis to reduce ATP production in cardiomyocytes
- Generating reactive oxygen species through NADPH oxidase activation
Correct answer: O-GlcNAc modification of transcription factors altering gene expression and causing endothelial dysfunction
Excess glucose flux through the hexosamine pathway leads to O-GlcNAc modification of proteins including transcription factors, altering expression of genes involved in endothelial function, plasminogen activator inhibitor-1, and TGF-beta.
Question 7: Diabetic cardiomyopathy can occur in the absence of coronary artery disease through which pathophysiologic mechanism?
- Hypoglycemic episodes causing repeated ischemia-reperfusion injury to myocytes
- Intramyocardial lipid accumulation and AGE-mediated myocardial fibrosis impairing diastolic function (Correct answer)
- Autonomic neuropathy increasing heart rate and reducing cardiac output chronically
- Hyperinsulinemia causing cardiomyocyte hypertrophy through IGF-1 receptor activation
Correct answer: Intramyocardial lipid accumulation and AGE-mediated myocardial fibrosis impairing diastolic function
Diabetic cardiomyopathy results from intramyocardial lipid deposition, AGE-mediated collagen cross-linking and fibrosis, and mitochondrial dysfunction, causing diastolic stiffness even without epicardial coronary disease.
CDE Pathophysiology 5
Maturity-onset diabetes of the young (MODY) is characterized by which distinctive genetic feature?