Question

Galactosemia is an inability to transform galactose into glucose and can lead to such problems as cataract formation, growth failure, mental retardation, or eventual death from liver damage. Galactose is reduced to galactitol, which initiates cataract formation. Accumulation of galactose 1 -phosphate, the most serious condition, leads to liver failure. The most severe form of galactosemia A. is a genetic deficiency of a uridylyltransferase that exchanges galactose 1 -phosphate for glucose on UDP-glucose. B. results from a deficiency of an epimerase. C. is insignificant in infants but a major problem in later life. D. is a defect in galactokinase. E. would be expected to interfere with the use of fructose as well as galactose because the deficient enzyme is common to the metabolism of both sugars.

Short answer

Answer: The most severe form of galactosemia is a genetic deficiency of a uridylyltransferase that exchanges galactose 1-phosphate for glucose on UDP-glucose.

Step-by-step solution

Review the options

Let's go through each option provided and assess if it represents the most severe form of galactosemia: A. is a genetic deficiency of a uridylyltransferase that exchanges galactose 1-phosphate for glucose on UDP-glucose. B. results from a deficiency of an epimerase. C. is insignificant in infants but a major problem in later life. D. is a defect in galactokinase. E. would be expected to interfere with the use of fructose as well as galactose because the deficient enzyme is common to the metabolism of both sugars.

Eliminate irrelevant options

We can eliminate options that don't directly relate to the severity of galactosemia: Option C: This does not specify a severe form of galactosemia, rather, it just mentions that it becomes a problem later in life. This doesn't answer the question, so we can eliminate option C. Option E: This option refers to the interference with the use of fructose and galactose, which could imply that it is severe but it doesn't specifically describe the most severe form of galactosemia. We can eliminate option E.

Evaluate the remaining options

Now, let's analyze the remaining options and choose the one that best describes the most severe form of galactosemia: Option A: This option describes a genetic deficiency in a uridylyltransferase enzyme, involved in the exchange of galactose 1-phosphate for glucose on UDP-glucose. This defect specifically refers to classic galactosemia (type I), which is the most severe form of this disorder. This is a strong candidate for the correct answer. Option B: This option refers to a deficiency of an epimerase, an enzyme involved in the conversion of one sugar to another. This would indicate galactosemia type III, which is less severe than classic galactosemia, as it impacts fewer processes in the body. Therefore, option B is not the most severe form of galactosemia. Option D: A defect in galactokinase describes galactokinase deficiency (galactosemia type II), which is a less severe form of the disorder than classic galactosemia, as it results in fewer complications. Thus, option D is not the most severe form of galactosemia.

Choose the correct answer

After reviewing the options, we can conclude that the most severe form of galactosemia: A. is a genetic deficiency of a uridylyltransferase that exchanges galactose 1-phosphate for glucose on UDP-glucose.

Key concepts

Understanding Genetic Deficiency in Galactosemia

Galactosemia is a rare genetic disorder that impacts how the body processes the simple sugar galactose. It arises from a genetic deficiency, meaning that a crucial gene is impaired or missing, leading to the inability to produce a functioning enzyme necessary for galactose metabolism. This genetic mutation can be inherited from parents, and it is often identified through newborn screening tests.

In galactosemia, particularly the most severe form, the deficiency occurs in the gene that encodes for the enzyme uridylyltransferase. Without this enzyme, toxic substances, including galactose 1-phosphate, accumulate in the body, leading to serious health issues like cataract formation, growth delays, intellectual disabilities, and life-threatening liver damage. The severity of symptoms often correlates with the degree of the enzyme deficiency; the more deficient the enzyme, the more severe the symptoms. Hence, understanding the genetic basis of galactosemia is crucial for early diagnosis and management of the condition.

Role of Uridylyltransferase in Galactose Metabolism

Uridylyltransferase, known scientifically as galactose-1-phosphate uridylyltransferase, plays a pivotal role in the conversion of galactose to glucose. This enzyme works by facilitating the transfer of a uridine diphosphate (UDP) from UDP-glucose to galactose 1-phosphate, effectively converting it into glucose 1-phosphate, which is a usable form of sugar for the body.

When a person is deficient in uridylyltransferase, galactose fails to undergo this essential metabolic conversion. Instead, it accumulates in various tissues, including the eyes, liver, and brain, causing the characteristic complications of galactosemia. Treatment usually involves dietary management, where dairy products and other galactose-containing foods are avoided to prevent the harmful build-up of sugars in the body. For elucidation, the exact genetic mutation causing uridylyltransferase deficiency can be identified through genetic testing, which is important for genetic counseling and understanding the inheritance pattern of the disorder.

Breaking Down Galactose Metabolism

Galactose metabolism is a critical biochemical pathway that enables the body to utilize galactose, which is found in milk, dairy products, and other foods. The process begins with the intake of lactose, a disaccharide consisting of glucose and galactose. Once ingested, lactose is broken down by the enzyme lactase into its component sugars.

Galactose is then converted into galactose 1-phosphate by the enzyme galactokinase. Subsequently, uridylyltransferase plays its role, as described above, to ultimately yield UDP-glucose and glucose 1-phosphate. These can then enter pathways for glycolysis or glycogen synthesis.

The metabolism of galactose is interconnected with that of glucose. Therefore, any disturbance, such as a deficiency of the enzymes galactokinase, epimerase, or uridylyltransferase, causes a break in the metabolic pathway, resulting in the accumulation of intermediates like galactose 1-phosphate. Effective management of galactosemia involves dietary adjustments to reduce galactose intake, supporting the liver's detoxification capacity, and monitoring for potential complications.