Question 1

Q: A 6-week-old infant presents with vomiting, jaundice, hepatomegaly, and cataracts. Urine reducing substances are positive, but glucose oxidase strip is negative. The infant is being breastfed. Red blood cell galactose-1-phosphate levels are markedly elevated. Based on the biochemical findings, which enzyme is most likely deficient?

Galactose-1-phosphate uridylyltransferase. ***Galactose-1-phosphate uridylyltransferase*** - Deficiency in this enzyme (GALT) leads to **Classic Galactosemia**, characterized by the accumulation of **galactose-1-phosphate**, which is toxic to the liver, kidneys, and brain. - Clinical presentation includes **jaundice**, **hepatomegaly**, and **vomiting** shortly after starting breast milk, along with positive **urine reducing substances** (galactose) and **cataracts**. *Galactokinase* - A deficiency in **galactokinase (GALK)** leads to the accumulation of **galactitol**, which causes isolated **cataracts** without systemic illness. - Unlike GALT deficiency, there is no accumulation of **galactose-1-phosphate**, so patients do not present with **liver failure** or **jaundice**. *UDP-glucose-4-epimerase* - This rare form of galactosemia can present similarly to the classic form but is usually distinguished by specific **isoenzyme** involvement. - While it can cause systemic symptoms, the **biochemical hallmark** in this clinical context specifically highlights the accumulation of **galactose-1-phosphate**, which directly points to GALT deficiency. *Phenylalanine hydroxylase* - Deficiency in this enzyme causes **Phenylketonuria (PKU)**, which presents with intellectual disability and a **mousy odor**, not acute neonatal liver failure. - PKU does not result in positive **urine reducing substances** or the formation of **cataracts** in early infancy. *Homogentisate oxidase* - This enzyme deficiency causes **Alkaptonuria**, a condition characterized by urine that turns black upon standing due to **homogentisic acid**. - It typically presents in adulthood with **ochronosis** and arthritis, rather than acute neonatal **vomiting** or **hepatomegaly**.

Question

A 6-week-old infant presents with vomiting, jaundice, hepatomegaly, and cataracts. Urine reducing substances are positive, but glucose oxidase strip is negative. The infant is being breastfed. Red blood cell galactose-1-phosphate levels are markedly elevated. Based on the biochemical findings, which enzyme is most likely deficient?

Accepted Answer

Galactose-1-phosphate uridylyltransferase

Answer

Galactokinase

Answer

UDP-glucose-4-epimerase

Answer

Phenylalanine hydroxylase

Answer

Homogentisate oxidase

Signal transduction pathways — MCQs

Signal transduction pathways — MCQs

On this page

Practice by Chapter

Want unlimited practice?