2025 – PAGE 362 – INBORN ERRORS OF METABOLISM & MISCELLANEOUS METABOLIC DISORDERS

INBORN ERRORS OF METABOLISM (IEM): For these disorders, look for sudden onset of lethargy, vomiting, tachypnea, seizures, and a lack of fever.
ORGANIC ACIDEMIAS: Look for TONS of messed up labs. Hyperammonemia, Ketosis, possible Thrombocytopenia, Lactic Acidosis, possible Granulocytopenia, and Hypoglycemia.
UREA CYCLE DEFECTS: Look for hypotonia and hyperammonemia, but that’s it! No acidosis, but possible respiratory alkalosis.
MITOCHONDRIAL DISORDERS: Includes fatty acid defects and GSD I. Since the powerhouse (mitochondria) is defective, look for evidence of anaerobic metabolism (elevated lactate and pyruvate). Uric acid is also elevated from protein break down. These are fuel problems, so HEPATOMEGALY is common. “Only a MOM can LACTATE.” Mito = Mom.
FATTY ACID OXIDATION DEFECTS: Symptomatic once glucose/glycogen reserves are depleted. Fatty acid catabolism is defective so there is NO ketosis, but there is acidosis (from lactate). There’s also hyperammonemia, possibly due to excessive protein breakdown for energy need.
STORAGE DISEASES: Slowly Present in late infancy or early childhood.
AMINO ACIDOPATHIES: No hyperammonemia because the urea cycle is fine, and there’s not excessive protein breakdown. No acidosis because there’s no sugar, fat, or energy/fuel issue.
- MSUD is the exception! Acidosis + Hypoglycemia + Hyperammonemia
HYPERGLYCINEMIA (“glycine encephalopathy”): Normal labs + Acute Encephalopathy + Hiccups+ Burst suppression on EEG.