Occurrence of GCH1 gene mutations in a group of Indian dystonia patients

Early-onset autosomal dominant GTP-cyclohydrolase I deficiency: Diagnostic delay and residual motor signs

OBJECTIVE

Autosomal dominant (AD) guanosine triphosphate cyclohydrolase 1 (GCH1) deficiency is the most common cause of dopa-responsive dystonia (DRD). Patients with GCH1 deficiency are likely to experience diagnostic delay, but its consequences have not been described thoroughly in patients with early-onset disease. We describe the diagnostic delay and residual motor signs (RMS) observed in patients with early-onset (before 15 years of age) disease.

METHODS

Twelve patients with early-onset AD GCH1 deficiency from a single center were included in the case series analysis. For the meta-analysis, the PubMed database was searched for articles on early-onset AD GCH1 deficiency published from 1995 to 2019.

RESULTS

In the case series, the mean duration of diagnostic delay was 5.6 years. Two patients exhibited RMS, and four patients underwent orthopedic surgery. The literature search yielded 137 AD GCH1 deficiency cases for review; gait disturbance was reported in 92.7% of patients, diurnal fluctuation of symptoms in 91.9%, and RMS in 39%. The mean duration of diagnostic delay was 14.6 years overall: 12.0 years in RMS-negative patients and 21.2 years in RMS-positive patients.

CONCLUSIONS

Diagnostic delay in early-onset AD GCH1 deficiency is more closely associated with later RMS. Early clinical suspicion, timely diagnosis, and levodopa treatment may reduce the occurrence of RMS in patients with early-onset AD GCH1 deficiency.

A Compound Heterozygote for GCH1 Mutation Represents a Case of Atypical Dopa-Responsive Dystonia

Dopa-responsive dystonia (DRD), a movement disorder, is characterized by young onset dystonia and dramatic response to levodopa treatment. However, the wide range of phenotypic spectrum of the disease often leads to misdiagnosis. DRD is usually caused by mutation in GCH1 gene coding for GTP cyclohydrolase 1 (GTPCH1) enzyme, which is involved in biosynthesis of tetrahydrobiopterin (BH4) and dopamine. In this study, the entire GCH1 gene was screened in 14 Indian DRD patients and their family members. A family was identified where the proband was found to be a compound heterozygote for GCH1 (p.R184H and p.V204I) variants; the former variant being inherited from the father and the latter from the mother. All other family members harboring one of these GCH1 variants were asymptomatic except for one (heterozygous for p.R184H) who was diagnosed with DRD. In silico analyses predicted these two variants to be pathogenic and disruptive to GCH1enzymatic activity. This proband was misdiagnosed as cerebral palsy and remained untreated for 25 years. He developed retrograde movements and gait problems in lower limbs, deformity in upper limbs, and difficulty in swallowing, and became mute. However, most of his symptoms were alleviated upon levodopa administration. Our study confirms the variability of DRD phenotype and the reduced penetrance of GCH1 mutations. It also emphasizes the need of molecular diagnostic test and L-dopa trial especially for those with atypical DRD phenotype.

Dopa-Responsive Dystonia in Han Chinese Patients: One Novel Heterozygous Mutation in GTP Cyclohydrolase 1 (GCH1) and Three Known Mutations in TH

Background

This study aimed to clarify the diagnosis and expand the understanding of dopa-responsive dystonia (DRD).

Material/Methods

Relevant data from clinical diagnoses and genetic mutational analyses in 3 Han Chinese patients with sporadic DRD were collected and analyzed. Protein structure/function was predicted.

Results

One novel mutation of c.679A>G (p.T227A) in GCH1 and 3 known mutations of c.457C>T (p.R153X), c.739G>A (p.G247S), and c.698G>A (p.R227H) in tyrosine hydroxylase (TH) have been found and predicted to be damaging or deleterious. All of the mutations were localized in conserved sequences. The iterative threading assembly refinement (I-TASSER) server generated three-dimensional (3D) atomic models based on protein sequences from the novel nonsense mutation of c.679A>G (p.T227A) in GCH1, which showed that residue 227 was located in the GCH1 active site.

Conclusions

Patients carrying different non-synonymous variants had remarkable variation in clinical phenotype. This study expands the spectrum of genotypes and phenotypes of DRD in the Han Chinese ethnicity, provides new insights into the molecular mechanism of DRD, and helps the diagnosis and treatment of DRD.

Interpretation of mRNA splicing mutations in genetic disease: review of the literature and guidelines for information-theoretical analysis

The interpretation of genomic variants has become one of the paramount challenges in the post-genome sequencing era. In this review we summarize nearly 20 years of research on the applications of information theory (IT) to interpret coding and non-coding mutations that alter mRNA splicing in rare and common diseases. We compile and summarize the spectrum of published variants analyzed by IT, to provide a broad perspective of the distribution of deleterious natural and cryptic splice site variants detected, as well as those affecting splicing regulatory sequences. Results for natural splice site mutations can be interrogated dynamically with Splicing Mutation Calculator, a companion software program that computes changes in information content for any splice site substitution, linked to corresponding publications containing these mutations. The accuracy of IT-based analysis was assessed in the context of experimentally validated mutations. Because splice site information quantifies binding affinity, IT-based analyses can discern the differences between variants that account for the observed reduced (leaky) versus abolished mRNA splicing. We extend this principle by comparing predicted mutations in natural, cryptic, and regulatory splice sites with observed deleterious phenotypic and benign effects. Our analysis of 1727 variants revealed a number of general principles useful for ensuring portability of these analyses and accurate input and interpretation of mutations. We offer guidelines for optimal use of IT software for interpretation of mRNA splicing mutations.

Interpretation of mRNA splicing mutations in genetic disease: review of the literature and guidelines for information-theoretical analysis

The interpretation of genomic variants has become one of the paramount challenges in the post-genome sequencing era. In this review we summarize nearly 20 years of research on the applications of information theory (IT) to interpret coding and non-coding mutations that alter mRNA splicing in rare and common diseases. We compile and summarize the spectrum of published variants analyzed by IT, to provide a broad perspective of the distribution of deleterious natural and cryptic splice site variants detected, as well as those affecting splicing regulatory sequences. Results for natural splice site mutations can be interrogated dynamically with Splicing Mutation Calculator, a companion software program that computes changes in information content for any splice site substitution, linked to corresponding publications containing these mutations. The accuracy of IT-based analysis was assessed in the context of experimentally validated mutations. Because splice site information quantifies binding affinity, IT-based analyses can discern the differences between variants that account for the observed reduced (leaky) versus abolished mRNA splicing. We extend this principle by comparing predicted mutations in natural, cryptic, and regulatory splice sites with observed deleterious phenotypic and benign effects. Our analysis of 1727 variants revealed a number of general principles useful for ensuring portability of these analyses and accurate input and interpretation of mutations. We offer guidelines for optimal use of IT software for interpretation of mRNA splicing mutations.

Treatable inborn errors of metabolism causing neurological symptoms in adults

BACKGROUND

The identification of inborn errors of metabolism (IEM) in adults presenting with a wide range of neurological symptoms is a relatively new field in medicine. We sought to identify which treatable IEM have been diagnosed for the first time in adults and generate a protocol for metabolic screening targeting those treatable disorders.

METHODS

Medline/Pubmed searches of English language literature limited to the adult age group were performed. Diseases identified through this search were then compared to previously published lists of treatable IEM in both adults and children.

RESULTS

85% of the treatable conditions known to cause global developmental delay or intellectual disability in children had reports where the diagnosis of that IEM was made in one or more adult patients with neurological symptoms. Screening tests in blood, urine, CSF and MRI can detect most of these treatable conditions but the diagnostic accuracy of these screening tests in adults is not clear.

CONCLUSION

Treatable IEM need to be considered in the differential diagnosis of neurological symptoms in patients of any age.

Dopa-Responsive Dystonia in a Ten-Year-Old Girl

Children with recent onset dystonia and gait abnormalities may pose a diagnostic challenge. A ten-year-old, developmentally normal girl, presented with a six-month history of gait abnormality and dystonia. Her complaint worsened as the day progressed. In view of typical diurnal variation of dystonia, a therapeutic challenge with levodopa/carbidopa was given and there was a dramatic response. Hence, a diagnosis of dopa-responsive dystonia (DRD) was made. DRD is an inherited disorder characterized by dystonia with diurnal variation and favorable response to levodopa/carbidopa. The inheritance is usually autosomal dominant, however, in some cases, autosomal-recessive inheritance is also seen.