A 2-year-old boy is brought to clinic because of poor development as well as vomiting, irritability, and a skin rash. The boy's mother also notes that his urine has a strange "mousy" odor. Physical examination reveals the child has an eczema-like rash, is hyperreflexive, and has increased muscle tone. He has a surprisingly fair-skinned complexion compared to the rest of his family. What is the most likely diagnosis?

Phenylketonuria: Phenyl ketone i.e. Phenyl Pyruvate found in urine of these patients (Pyruvate is a Keto-acid). Affected children are normal at bih but fail to reach developmental milestones Clinical features: Body odour - mousy or musty because of phenylacetate. Severe mental retardation due to excess Phenylalanine. Tyrosine becomes essential Deficiency of pigment Melanin (formed from Tyrosine), leads to fair skin, blue eyes and light hair color. OTHER FEATURES: Microcephaly, rash, hypeoma, seizures, hyperactivity, exaggerated tendon reflexes, wide-spaced teeth, enamel hypoplasia. Rx:- Decreased dietary phenylalanine (which is contained in many foods, including aificial sweeteners). Dietarytyrosine supplementation(In patients with pKU, tyrosine cannot be derived from phenylalanine) Currently, screeningis mandatory and performed6 days to 2 weeksafter bih using high-performance liquid chromatography.