Which inherited disorder occurs when an infant lacks a specific liver enzyme?

Phenylketonuria (PKU) is an inherited metabolic disorder characterized by the absence or deficiency of the enzyme phenylalanine hydroxylase. This enzyme is crucial for the metabolism of the amino acid phenylalanine, which is found in many protein-containing foods. When this enzyme is lacking or dysfunctional, phenylalanine accumulates in the bloodstream, leading to potential intellectual disability and other neurological issues if not managed properly.

Early diagnosis and treatment, typically through dietary restrictions that limit phenylalanine intake, are essential for preventing the adverse effects associated with this condition. The identification of PKU typically occurs through newborn screening programs, emphasizing the importance of early intervention.

The other options relate to different contexts: muscular dystrophy is a group of genetic diseases characterized by progressive muscle degeneration; endothelium refers to the thin layer of cells lining blood vessels; and dense regular connective tissue consists of tightly packed collagen fibers found in tendons and ligaments. These terms do not pertain to metabolic enzyme deficiencies or inherited disorders like PKU.