What is one possible cause of neonatal jaundice that appears within 24 hours after birth?

Neonatal jaundice that appears within the first 24 hours after birth is often due to underlying physiological factors that disrupt the normal metabolism of bilirubin. Congenital hepatic conjugation defects are conditions that impede the liver's ability to conjugate bilirubin, leading to an accumulation of unconjugated bilirubin in the bloodstream. This early onset jaundice is typically a sign of a more serious underlying condition, such as Crigler-Najjar syndrome or Gilbert syndrome, both of which are genetic disorders that affect bilirubin processing.

In contrast, the other options generally do not present as early as within the first 24 hours. Hypothyroidism can lead to jaundice, but this typically develops after a few days. Breast milk jaundice develops later, usually around the first week of life, due to substances in breast milk that may interfere with bilirubin metabolism. Galactosaemia may present with jaundice but typically has other associated symptoms like feeding difficulties and vomiting, which may arise after a short time. Therefore, congenital hepatic conjugation defects are specifically linked to the early appearance of jaundice in neonates within the first day after birth.