Gene mutation in hereditary progressive dystonia with marked diurnal fluctuation (HPD), strictly defined dopa-responsive dystonia

A Case of GCH-1 Mutation Dopa-Responsive Dystonia Requiring High Doses of Levodopa for Treatment

Background:

Mutations in the GCH-1 gene are associated with Autosomal Dominant Dopamine Responsive Dystonia (DYT 5). One of the hallmarks of this condition is dramatic and sustained response to low doses of levodopa.

Case Report:

We present the case of a 22 year old female patient with genetically confirmed GCH-1 Dopa-Responsive Dystonia who had no response to low dose Levodopa but who achieved symptom control on a total dose of 900 mg/day.

Discussion:

Autosomal Dominant Dopa-Responsive Dystonia is a phenotypical heterogenous condition that, in some cases, may require high doses of levodopa for treatment response.

Highlights

Mutations in the GCH-1 gene are associated with Autosomal Dominant Dopamine Responsive Dystonia which is typically defined by dramatic responses to low doses of levodopa. We report a patient with genetically confirmed Dopa-Responsive Dystonia who had no response to low dose Levodopa but who achieved symptom control with 900 mg/day.

Dopa-responsive dystonia: functional analysis of single nucleotide substitutions within the 5' untranslated GCH1 region

Background

Mutations in the GCH1 gene are associated with childhood onset, dopa-responsive dystonia (DRD). Correct diagnosis of DRD is crucial, given the potential for complete recovery once treated with L-dopa. The majority of DRD associated mutations lie within the coding region of the GCH1 gene, but three additional single nucleotide sequence substitutions have been reported within the 5’ untranslated (5’UTR) region of the mRNA. The biologic significance of these 5’UTR GCH1 sequence substitutions has not been analyzed.

Methodology/Principal Findings

Luciferase reporter assays, quantitative real time PCR and RNA decay assays, combined with bioinformatics, revealed a pathogenic 5’UTR GCH1 substitution. The +142C>T single nucleotide 5’UTR substitution that segregates with affected status in DRD patients, substantially attenuates translation without altering RNA expression levels or stability. The +142C>T substitution disrupts translation most likely by creating an upstream initiation start codon (uAUG) and an upstream open reading frame (uORF).

Conclusions/Significance

This is the first GCH1 regulatory substitution reported to act at a post-transcriptional level, increasing the list of genetic diseases caused by abnormal translation and reaffirming the importance of investigating potential regulatory substitutions in genetic diseases.

Dopa-responsive dystonia

Clinical characteristics and pahophysiologies of dopa-responsive dystonia are discussed by reviewing autosomal-dominant GTP cyclohydrolase-I deficiency (AD GCHI D), recessive deficiencies of enzymes of pteridine metabolism, and recessive tyrosine hydroxylase (TH). Pteridine and TH metabolism involve TH activities in the terminals of the nigrostriatal dopamine neuron which show high in early childhood and decrease exponentially with age, attaining stational low levels by the early 20s. In these disorders, TH in the terminals follows this course with low levels and develops particular symptoms with functional maturation of the downstream structures of the basal ganglia; postural dystonia through the direct pathway and descending output matured earlier in early childhood and parkinsonism in TH deficiency in teens through the D2 indirect pathway ascending output matured later. In action-type AD GCHI D, deficiency of TH in the terminal on the subthalamic nucleus develops action dystonia through the descending output in childhood, focal and segmental dystonia and parkinsonism in adolescence and adulthood through the ascending pathway maturing later. Dysfunction of dopamine in the terminals does not cause degenerative changes or higher cortical dysfunction. In recessive disorders, hypofunction of serotonin and noradrenaline induces hypofunction of the dopamine in the perikaryon and shows cortical dysfunction.

A novel missense mutation of the GTP cyclohydrolase I gene in a Korean family with hereditary progressive dystonia/dopa-responsive dystonia

Hereditary progressive dystonia with marked diurnal fluctuation/dopa-responsive dystonia (HPD/DRD) shows the considerable heterogeneity of clinical phenotypic expression and a dramatic sustained response to levodopa. The autosomal dominant HPD/DRD is caused by mutations in the gene coding GTP cyclohydrolase I (GCH I), the enzyme that catalyzes the first step in the biosynthesis of tetrahydrobiopterin. Previous studies suggested that normal [18F]Dopa positron emission tomography or [123I]beta-CIT single-photon emission computed tomography (SPECT) imaging, indicating intact structural integrity of nigrostriatal neurons, may be useful for differentiating HPD/DRD from clinically similar conditions such as juvenile Parkinson's disease with dystonia that have a considerably poorer prognosis. We here report a Korean family affected with HPD/DRD due to a novel missense mutation of the GCH I gene (T-->G mutation in exon 2), Met 137 Arg, which may change the conformation of the binding site of GCH I. The clinical features are considerably variable within the family. We documented normal striatal uptake of [123I]IPT, a dopamine transporter ligand with fast washout kinetics, in our patients by using SPECT. This method can be helpful in diagnosing HPD/DRD in uncertain cases.

Transgenic mouse models of dopamine deficiency

The dopamine system is implicated in several neurological and psychiatric disorders. Genetic mutations or variations that affect dopamine system functions either directly cause or contribute to these disorders, even though other genetic and environmental factors may contribute significantly to some of these disorders as well. Transgenic mice increasingly become important tools in revealing functions of genes that are essential components of the dopamine system as well as in modeling human genetic disorders. We have reviewed a comprehensive list of those genes and compared genetic mutations/variations in humans and transgenic mouse models. The significance and limitations of these animal models as well as future directions are discussed.

[Movement disorders in childhood: classification and genetic update]

Abnormal movements are not unusual in childhood. Recent genetic progresses provide a new approach of childhood movement disorders. Several loci have been identified in paroxysmal dyskinesia, or in Gilles de la Tourette syndrome. A gene has been cloned in Hallervorden-Spatz syndrome, and a gene has recently been implicated in benign hereditary chorea. Considerable advances concern the genetic of dystonic syndromes: several chromosomal localizations have been identified, and several genes have been cloned. Genetic advances allow nosographic reclassification of some entities and offer new molecular tools for a more appropriate diagnosis. The increasing wealth of genetic knowledge will provide further insight in the understanding of abnormal movement disorders in childhood.

Childhood onset generalised dystonia can be modelled by increased gain in the indirect basal ganglia pathway

Clinical experience suggests an important role of the indirect basal ganglia pathway in the genesis of childhood onset generalised dystonia, but it has been difficult to reconcile the increased muscle activity in dystonia with the current model of basal ganglia function in which the indirect pathway is considered primarily inhibitory. The aim of this study was to present a modification of the direct-indirect pathway model, in which the indirect pathway is inverting rather than purely inhibitory, so that while high signals are inhibited, low signals are amplified. As the basal ganglia may be a feedback loop that modifies cortical activity, instability from excessive gain in this feedback loop could explain features of dystonia. A detailed mathematical model is provided, together with simulations of cortical cell population spiking behaviour when connected through a basal ganglia loop. The simulations show that increased gain in the indirect pathway relative to the direct pathway can lead to unstable uncontrolled synchronous oscillations in cortex and basal ganglia. This behaviour could result in dystonia. The model provides a consistent explanation for the association of dystonia with parkinsonism and disorders characterised by dopamine depletion, the ability to treat some dystonias with dopamine, the ability of neuroleptic drug treatment to cause an acute dystonic reaction treatable with anticholinergic drugs, and the ability of pallidotomy or deep brain stimulation of the internal pallidum to alleviate symptoms of generalised dystonia.

Hereditary progressive dystonia with marked diurnal fluctuation

Hereditary progressive dystonia with marked diurnal fluctuation or the strictly defined dopa-responsive dystonia (HPD/DRD) is an autosomally dominantly inherited dystonia caused by abnormalities of the gene of the GTP cyclohydrolase I (GCH 1) located on the 14q22. 1-q22.2. The heterozygotic gene abnormality induces partial decrement of tetrahydrobiopterin (BH4) and affects synthesis of tyrosine hydroxylase (TH) rather selectively. The reduction of TH exists at the terminals of the nigrostriatal (NS) dopamine (DA) neuron, predominantly in the ventral area of the striatum and disfacilitates the D1 receptor-striatal direct pathway. This consequently disinhibit the inhibitory efferent pathways and develops postural dystonia via the particular descending pathways to the reticulospinal tract and postural tremor via the ascending pathways to the ventralis lateralis (VL) nucleus of the thalamus. This also inhibits the efferents to the superior colliculus, and affects voluntary saccade but spares that to the pedunculo-pontine nucleus (PPN) preserving locomotive movement clinically. The DA-D2 receptors, the striatal indirect pathways or the efferent connecting to these pathways are not involved in the pathophysiology of HPD/DRD. So parkinsonian plastic rigidity, parkinsonian resting tremor, cogwheel rigidity or levodopa induced dyskinesia are not observed. In some patients, particularly in compound hetereozygotes, there are symptoms suggesting the involvement of serotonergic neurons or those thought to be caused by exaggeration of DA-D2 receptors. Neuropathologically there is no degenerative changes. Clinical laboratory examinations suggest that levels of TH and DA activities are around 20% of the normal values throughout the course of illness. Therefore, the age-dependent clinical course, marked progression in the first one and one half decades, its subsiding in the third decade and almost stationary course from the fourth decade are just the reflection of age-related decremental variation of the TH activities at the terminal of the normal NS-DA neuron. The diurnal fluctuation is also the reflection of circadian oscillation of the TH activities at the terminal. Functional maturation of the striatal indirect pathways in the first one and one half decades and developmental decremental variation of the DA-D2 receptor in the first three decades also reflect in the age-dependent variation of symptoms by modulating the background tone of muscle. The later functional development of the ascending efferents of the basal ganglia to the thalamus, may cause the postural tremor which appears in the second decade and becomes predominant in the fourth decade. Early decrease of TH due to deficiency of BH4 in HPD/DRD also affects the DA-D4 receptor of the tuberoinfundibular DA neuron and cause stagnation of increase of body length in childhood. With normal preservation of the fundamental function of the NS-DA neuron, levodopa, by replacing the DA content at the terminal, alleviates the motor symptoms completely and the effects sustain without any side effects. Levodopa also improves the short body length, if it is administrated before puberty. Up to now 60 mutations have been detected in the GCH 1 gene. The locus of mutation differs among families except for two pare of families with different ethnic background which showed identical mutations. Experimentally, one abnormal heterozygotic gene decreased the production of the enzyme to less than 50%, e.g. some below 20% and others around 30-40%, which clinically as symptomatic patients and asymptomatic carriers, respectively. Other experiments show dominant negative effects which differ among families or the loci of mutation. These might be the background for developing the intra-familial variation, that is, in some there is anticipation, and in the other the symptoms and clinical course are identical or vary in a family without any relation to the generation. (ABSTRACT TRUNCATED)