Method modification to reduce false positives for newborn screening of guanidinoacetate methyltransferase deficiency.

Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessive disorder that results in reduced activity of guanidinoacetate methyltransferase, an accumulation of guanidinoacetate (GUAC), and a lack of cerebral creatine (CRE). Lack of CRE in the brain can cause intellectual disability, autistic-like behavior, seizures, and movement disorders. Identification at birth and immediate therapy can prevent intellectual disability and seizures.