An infant present with hypotonia and seizures. It was confirmed to be cerebrohepatorenal syndrome. Which of the following is accumulated in the brain in cerebrohepatorenal syndrome?

Explanation

## Correct Answer: B. Long chain fatty acid Cerebrohepatorenal syndrome (Zellweger syndrome) is a peroxisomal biogenesis disorder caused by defects in peroxisomal assembly. Peroxisomes are essential organelles responsible for **β-oxidation of very long chain fatty acids (VLCFAs)** (>20 carbons). In Zellweger syndrome, absent or severely defective peroxisomes cannot metabolize VLCFAs, leading to their pathological accumulation in tissues, particularly the brain, liver, and kidneys. The accumulated long-chain fatty acids (especially C26:0 and C24:0) are neurotoxic and cause demyelination, neuronal dysfunction, and the characteristic clinical features: severe hypotonia ("floppy infant"), seizures, developmental delay, and hepatomegaly. The diagnosis is confirmed by elevated plasma VLCFA levels (especially hexacosanoic acid/C26:0) and absent peroxisomes on electron microscopy. This is an autosomal recessive condition with poor prognosis; most infants die within the first year. The biochemical hallmark is VLCFA accumulation, not lactate, glucose, or triglycerides, which are metabolized through other pathways unaffected in this disorder. ## Why the other options are wrong **A. Lactic acid** — Lactic acidosis occurs in mitochondrial disorders (e.g., MELAS, pyruvate dehydrogenase deficiency) and organic acidemias, not peroxisomal disorders. While Zellweger syndrome causes neurological symptoms, the primary metabolic defect is peroxisomal β-oxidation failure, not impaired aerobic metabolism. Lactate accumulation is not a biochemical marker of Zellweger syndrome. **C. Glucose** — Glucose metabolism is normal in Zellweger syndrome; glycolysis and gluconeogenesis are intact. Hypoglycemia may occur secondary to hepatic dysfunction, but glucose itself does not accumulate in the brain. This option confuses metabolic complications with the primary enzymatic defect. **D. Triglycerides** — Triglycerides are metabolized via lipoprotein lipase and mitochondrial β-oxidation, pathways that remain functional in Zellweger syndrome. While hepatomegaly occurs due to lipid accumulation, the specific accumulating lipids are unesterified long-chain fatty acids, not triglycerides. This option represents a common misconception about lipid storage disorders. ## High-Yield Facts - **Zellweger syndrome** is caused by peroxisomal biogenesis defects (PEX gene mutations), leading to absent or dysmorphic peroxisomes. - **Very long chain fatty acids (C>20)** accumulate in plasma and tissues because peroxisomes cannot perform β-oxidation; diagnosis confirmed by elevated C26:0 (hexacosanoic acid). - **Cerebrohepatorenal triad**: severe CNS involvement (hypotonia, seizures, developmental delay), hepatomegaly, and renal cysts are pathognomonic. - **Peroxisomes** are the only organelles capable of initiating β-oxidation of VLCFAs; mitochondria complete the process for shorter chains. - **Prognosis**: most infants die within 6–12 months; no cure exists; management is supportive (seizure control, nutritional support). ## Mnemonics **PEX = Peroxisomal Enzyme eXplosion** PEX gene mutations → peroxisomes absent/defective → VLCFA cannot be oxidized → accumulate in brain/liver/kidney. Use this when you see 'cerebrohepatorenal' to remember the three organs affected. **VLCFA = Very Long Chain Fatty Acid (>C20)** Only peroxisomes can START β-oxidation of VLCFA; mitochondria finish the job. In Zellweger, the START fails → accumulation. Remember: peroxisomes = the 'starter' organelle for long chains. ## NBE Trap NBE pairs "cerebrohepatorenal syndrome" with seizures and hypotonia to tempt students toward mitochondrial disorders (lactic acidosis) or glycogen storage diseases (glucose). The trap is forgetting that Zellweger is a **peroxisomal** disorder, not a mitochondrial one, and that the specific metabolic defect is VLCFA accumulation, not lactate or glucose. ## Clinical Pearl In Indian neonatal units, Zellweger syndrome presents as a "floppy infant" with seizures and hepatomegaly in the first weeks of life—a medical emergency requiring immediate metabolic workup (plasma VLCFA, very long chain fatty acid profile) and seizure management. Early recognition prevents misdiagnosis as cerebral palsy or primary seizure disorder. _Reference: Robbins Ch. 5 (Genetic Disorders); Harper's Biochemistry Ch. 27 (Lipid Transport & Storage); KD Tripathi Pharmacology (Peroxisomal Disorders)_