Galactosemia is characterized by the inability to produce which substance?

Galactosemia is a genetic metabolic disorder that affects the body's ability to process galactose, which is a type of sugar found in milk and dairy products. In individuals with galactosemia, there is a deficiency in the enzyme galactose-1-phosphate uridyltransferase (GALT) or other enzymes involved in galactose metabolism. As a result, galactose builds up in the blood, leading to various health complications. The condition is specifically marked by this inability to metabolize galactose effectively, rather than issues with other sugars like sucrose, lactose, or fructose. Thus, the correct answer is that galactosemia is characterized by the inability to produce or effectively use galactose.