A male child presents with progressive skeletal myopathy, episodes of hypoketotic hypoglycemia, and cardiomyopathy, worsened by fasting. Plasma carnitine is very low. Urine organic acids show minimal ketones but elevated dicarboxylic acids. The likely diagnosis is:
- A Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency
- B Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency
- C Primary carnitine deficiency (OCTN2 transporter mutation) ✓
- D Multiple acyl-CoA dehydrogenase deficiency (glutaric aciduria type II)
Explanation
Primary carnitine deficiency results from mutations in the OCTN2 sodium-dependent carnitine transporter, causing failure of cellular carnitine uptake in muscle, heart, and kidney. Without carnitine, long-chain fatty acids cannot enter mitochondria for beta-oxidation, leading to hypoketotic hypoglycemia, myopathy, and cardiomyopathy. Urine shows dicarboxylic aciduria from peroxisomal omega-oxidation of unoxidized fatty acids. MCAD deficiency causes medium-chain dicarboxylates and is not associated with cardiomyopathy or low plasma carnitine as the primary defect. VLCAD deficiency can be similar but plasma carnitine is usually normal.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.