Affiliation:
1. Child Neurology and Psychiatry Unit, Department of Human Neurosciences Sapienza University of Rome Rome Italy
2. Clinical Pathology Unit, Department of Experimental Medicine AOU Policlinico Umberto I‐Sapienza University Rome Italy
3. Movement Disorders Program, Department of Neurology Boston Children's Hospital, Harvard Medical School Boston Massachusetts USA
Abstract
AbstractBackgroundThe GCH1 gene encodes the enzyme guanosine triphosphate cyclohydrolase I (GTPCH), which catalyzes the rate‐limiting step in the biosynthesis of tetrahydrobiopterin (BH4), a critical cofactor in the production of monoamine neurotransmitters. Autosomal dominant GTPCH (adGTPCH) deficiency is the most common cause of dopa‐responsive dystonia (DRD), whereas the recessive form (arGTPCH) is an ultrarare and poorly characterized disorder with earlier and more complex presentation that may disrupt neurodevelopmental processes. Here, we delineated the phenotypic spectrum of ARGTPCHD and investigated the predictive value of biochemical and genetic correlates for disease outcome.ObjectivesThe aim was to study 4 new cases of arGTPCH deficiency and systematically review patients reported in the literature.MethodsClinical, biochemical, and genetic data and treatment response of 45 patients are presented.ResultsThree phenotypes were outlined: (1) early‐infantile encephalopathic phenotype with profound disability (24 of 45 patients), (2) dystonia‐parkinsonism phenotype with infantile/early‐childhood onset of developmental stagnation/regression preceding the emergence of movement disorder (7 of 45), and (3) late‐onset DRD phenotype (14 of 45). All 3 phenotypes were responsive to pharmacological treatment, which for the first 2 must be initiated early to prevent disabling neurodevelopmental outcomes. A gradient of BH4 defect and genetic variant severity characterizes the 3 clinical subgroups. Hyperphenylalaninemia was not observed in the second and third groups and was associated with a higher likelihood of intellectual disability.ConclusionsThe clinical spectrum of arGTPCH deficiency is a continuum from early‐onset encephalopathies to classical DRD. Genotype and biochemical alterations may allow early diagnosis and predict clinical severity. Early treatment remains critical, especially for the most severe patients.