Expanding Phenotype of ATP1A3 - Related Disorders: A Case Series

Neurologic disorders caused by mutations in the ATP1A3 gene were originally reported as three distinct rare clinical syndromes: Alternating Hemiplegia of Childhood (AHC), Rapid-onset Dystonia Parkinsonism (RDP) and Cerebellar ataxia, Areflexia, Pes cavus, Opticus atrophy and Sensorineural hearing loss (CAPOS). In this case series, we describe 3 patients. A mother and her daughter showed an intermediate phenotype different from each other with the same heterozygous missense mutation (p.[R756C]), recently described in literature as Relapsing Encephalopathy With Cerebellar Ataxia (RECA). In addition, a third patient showed an intermediate AHC-RDP phenotype and had a likely pathogenic novel de novo missense mutation (p.[L100 V]). These patients support the growing evidence that AHC, RDP and RECA are part of a continuous ATP1A3 mutation spectrum that is still expanding. Three common features were a sudden onset, asymmetrical neurological symptoms, as well as the presence of triggering factors. When present, the authors argue to perform exome sequencing in an early stage.

Biochemical hallmarks of tyrosine hydroxylase deficiency

We report the biochemical hallmarks of tyrosine hydroxylase deficiency with emphasis on reliable diagnostic strategies of four new cases of an inborn error of tyrosine hydroxylase (TH). Three of our patients from different parts of the Netherlands were found homozygous for a mutation in exon 6 (G698A) of the TH gene, and one patient was found compound heterozygous for the same mutation and an additional mutation in exon 3. The first clinical symptoms of hypokinesia, rigidity of arms and legs and axial hypotonia, developed between 3 and 7 months of age. Cerebrospinal fluid investigations revealed a characteristic metabolite constellation in every case: low homovanillic acid (HVA) and 3-methoxy-4-hydroxy-phenylethyleneglycol concentrations in the presence of normal reference range 5-hydroxyindolacetic acid concentrations. Strict adherence to a standardized lumbar puncture protocol and adequate age-related reference values are essential for diagnosis of this “new” treatable neurometabolic disorder. Urinary measurements of HVA, vanillylmandelic acid, and catecholamines can lead to false-negative conclusions. All patients showed a remarkable clinical improvement on a low dose of l-dihydroxyphenylalanine/(S)-2-(3,4-dihydroxybenzyl)-2-hydrazinpropionic acid. During treatment, cerebrospinal fluid HVA, and 3-methoxy-4-hydroxy-phenylethyleneglycol increased substantially.