Topic overview

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Many of these disorders are inherited in an autosomal-recessive pattern, and early recognition matters because untreated metabolic disturbances can cause lasting neurological or systemic harm. The topic connects specific biochemical defects with characteristic findings—for example, phenylalanine hydroxylase deficiency in PKU, branched-chain amino-acid metabolism impairment in MSUD, and cystathionine-β-synthase deficiency in homocystinuria. It also introduces maternal PKU and fetal risks, disorders of organic acid metabolism, amino-acid transport defects, and OTC deficiency. Newborn tandem mass spectrometry can identify abnormal amino- and organic-acid profiles. Management principles include targeted dietary restriction and, where applicable, therapies such as BH4, thiamine, biotin, or B vitamins.