Moreover, GTP cyclohydrolase I deficiency can also follow an autosomal recessive inheritance pattern (OMIM#233910), with or without hyperphenylalaninemia, typically associated with a more complex presentation and more severe clinical manifestations, including truncal hypotonia, neonatal-onset rigidity, tremor, dystonia, spasticity, and oculogyric crises [59]. Here, GCH1 is linked to Dystonia.