Deficient secretion of bilirubin into bile canaliculi is seen in which syndrome?

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Defective export of conjugated bilirubin from hepatocytes into the bile canaliculi leads to conjugated (direct) hyperbilirubinemia. In Dubin-Johnson syndrome this excretion step is blocked because of mutations in the canalicular transporter MRP2 (ABCC2). As a result, conjugated bilirubin accumulates in the liver cells and spills into the bloodstream, producing intermittent jaundice with predominantly direct bilirubin elevations. The liver often appears dark on gross exam due to pigment deposition, and the condition is inherited in an autosomal recessive pattern.

Gilbert's disease involves reduced activity of UDP-glucuronosyltransferase, causing unconjugated bilirubin buildup, not a canalicular export defect. Neonatal hyperbilirubinemia is typically due to immature conjugation affecting mainly unconjugated bilirubin. Crigler-Najjar syndrome is a severe deficiency of the same conjugation enzyme, also leading to unconjugated hyperbilirubinemia rather than impaired canalicular secretion.