3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD) is an inherited metabolic disorder caused by mutations in the MCCC1 or MCCC2 genes, which prevent the body from properly breaking down the amino acid leucine. This autosomal recessive condition exhibits a broad clinical spectrum, ranging from asymptomatic individuals to those suffering from severe metabolic crises characterised by vomiting, low blood sugar, and neurological distress. Diagnosis is primarily achieved through newborn screening by detecting elevated C5OH levels in blood spots, though confirmatory genetic and urine testing is often required. While there is no cure, patients typically manage the condition using a low-protein diet, avoiding fasting, and taking L-carnitine supplements to prevent deficiency. Research indicates that while a diagnosis initially causes significant parental anxiety, this psychological burden tends to decrease as families receive education and specialist support. Ultimately, medical experts suggest that the benefits of early detection in preventing fatal complications outweigh the emotional challenges faced by families.