Which pair correctly describes two metabolic disorders that can present with seizures in infancy and a diagnostic clue for each?

• A. Rett Syndrome — Language Regression; Duchenne Muscular Dystrophy — Decreased Reflexes
• B. Porencephaly — Headaches; Spinal Muscular Atrophy — Hyperkalemia
• C. Pyridoxine-Dependent Epilepsy — Seizures Responsive to Vitamin B6; Pyruvate Dehydrogenase Deficiency — Lactic Acidosis With Elevated Lactate On Labs
• D. Pyruvate Dehydrogenase Deficiency — Lactic Acidosis With Elevated Lactate On Labs; Porencephaly — Headaches; Spinal Muscular Atrophy — Hyperkalemia

Answer: (C)

Infantile seizures from metabolic disorders often come with distinctive clues that point to the underlying problem and guide treatment.

Pyridoxine-dependent epilepsy is characterized by seizures that dramatically respond to vitamin B6, making the clue the seizure improvement with pyridoxine administration. Pyruvate dehydrogenase deficiency disrupts the ability to convert pyruvate to acetyl-CoA, leading to lactic acidosis; the diagnostic clue is a persistent lactic acidosis with elevated lactate on laboratory testing. Together, these two disorders are classic examples of metabolic causes of seizures in infancy with clear, actionable diagnostic hints.

Other options mix conditions that aren’t primarily metabolic epilepsies or pair clues that aren’t characteristic for infancy, such as structural brain issues or neuromuscular diseases that don’t present with the same metabolic seizure clues.