American Board of Genetic Counseling (ABGC) Boards Practice Test

In individuals with homocystinuria, the key biochemical marker that is elevated is homocysteine. Homocystinuria is a genetic disorder that affects the metabolism of methionine, an amino acid. The body is unable to properly convert homocysteine to cystathionine due to a deficiency in the enzyme cystathionine beta-synthase or, in some cases, other enzymes involved in the same metabolic pathway. As a result, homocysteine accumulates in the blood and can lead to various health issues, including cardiovascular problems and neurological complications.

The other options do not relate to homocystinuria specifically. Leucine is an amino acid that does not have a direct connection to this condition. Galactocerebroside is a type of glycolipid involved in cell membranes, particularly in the nervous system, and is associated with different metabolic disorders such as Krabbe disease. Psychosine, another lipid component, is linked with the same conditions as galactocerebroside, notably in the context of Krabbe disease as well. Therefore, the unique elevation of homocysteine serves as a crucial diagnostic marker for identifying homocystinuria in patients.