Question

An 18-month old male baby has been having reoccurring infections for the last year and is now starting to show neurological complications. Genetic testing shows a defect for a metabolic enzyme. The child’s ammonia and uric acid levels are normal. Blood pH is 7.41. The kidney function is also normal. A defect in which of the following enzymes is most likely to show the above symptoms?

a. Purine nucleoside phosphorylase
b. Xanthine oxidase
c. D-amino acid oxidase
d. Arginase
e. Phenylalanine hydroxylase

Answer 1

There is a defect in Purine nucleoside phosphorylase enzyme in that child.

Explanation:

• This enzyme helps in Purine metabolism. It converts inosine to hypoxanthine and guanosine to guanine.

• The deficiency of this enzyme causes immunodeficiency disorder where the immune system is unable to protect our body properly from foreign pathogens such as bacteria and viruses.

• Some people have a low amount of T cells because of the deficiency of this enzyme. T cell recognizes the pathogens and attacks them to prevent infection.
• Some people have a low amount of B cells, which helps us to fight against the infections by producing antibodies or immunoglobulins. Antibodies target foreign pathogens and destroy them.
• Some very affected individuals lack both T cells and B cells. They go through have a serious condition known as severe combined immunodeficiency (SCID).