Ara Kaprelyan

Autosomal-Recessive Congenital Cerebellar Ataxia Is Caused by Mutations in Metabotropic Glutamate Receptor 1

Autosomal-recessive congenital cerebellar ataxia was identified in Roma patients originating from a small subisolate with a known strong founder effect. Patients presented with global developmental delay, moderate to severe stance and gait ataxia, dysarthria, mild dysdiadochokinesia, dysmetria and tremors, intellectual deficit, and mild pyramidal signs. Brain imaging revealed progressive generalized cerebellar atrophy, and inferior vermian hypoplasia and/or a constitutionally small brain were observed in some patients. Exome sequencing, used for linkage analysis on extracted SNP genotypes and for mutation detection, identified two novel (i.e., not found in any database) variants located 7 bp apart within a unique 6q24 linkage region. Both mutations cosegregated with the disease in five affected families, in which all ten patients were homozygous. The mutated gene, GRM1, encodes metabotropic glutamate receptor mGluR1, which is highly expressed in cerebellar Purkinje cells and plays an important role in cerebellar development and synaptic plasticity. The two mutations affect a gene region critical for alternative splicing and the generation of receptor isoforms; they are a 3 bp exon 8 deletion and an intron 8 splicing mutation (c.2652_2654del and c.2660+2T>G, respectively [RefSeq accession number NM_000838.3]). The functional impact of the deletion is unclear and is overshadowed by the splicing defect. Although ataxia lymphoblastoid cell lines expressed GRM1 at levels comparable to those of control cells, the aberrant transcripts skipped exon 8 or ended in intron 8 and encoded various species of nonfunctional receptors either lacking the transmembrane domain and containing abnormal intracellular tails or completely missing the tail. The study implicates mGluR1 in human hereditary ataxia. It also illustrates the potential of the Roma founder populations for mutation identification by exome sequencing.

GNE myopathy in Roma patients homozygous for the p.I618T founder mutation

GNE myopathy is an autosomal-recessive disorder caused by mutations in the GNE gene, encoding the key enzyme in the sialic acid biosynthetic pathway, UDP-N-acetylglucosamine 2-epimerase/N-acetyl mannosamine kinase. We studied 50 Bulgarian Roma patients homozygous for p.I618T, an ancient founder mutation in the kinase domain of the GNE gene, dating before the Gypsy exodus from North West India. The clinical features in the Bulgarian GNE group can be described with disease onset mostly in the third decade, but in individual cases, onset was as early as 10 years of age. The majority of patients had foot drop as the first symptom, but three patients developed hand weakness first. Muscle weakness was early and severe for the tibialis anterior, and minimal or late for quadriceps femoris, and respiratory muscles were only subclinically affected even in the advanced stages of the disease. During a 15-year follow-up period, 32 patients became non-ambulant. The average period between disease onset and loss of ambulation was 10.34 ± 4.31 years, ranging from 3 to 20 years. Our analysis of affected sib pairs suggested a possible role of genetic modifying factors, accounting for significant variation in disease severity.

Transcriptome-wide effects of a POLR3A gene mutation in patients with an unusual phenotype of striatal involvement

RNA polymerase III is essential for the transcription of non-coding RNAs, including tRNAs. Mutations in the genes encoding its largest subunits are known to cause hypomyelinating leukodystrophies (HLD7) with pathogenetic mechanisms hypothesised to involve impaired availability of tRNAs. We have identified a founder mutation in the POLR3A gene that leads to aberrant splicing, a premature termination codon and partial deficiency of the canonical full-length transcript. Our clinical and imaging data showed no evidence of the previously reported white matter or cerebellar involvement; instead the affected brain structures included the striatum and red nuclei with the ensuing clinical manifestations. Our transcriptome-wide investigations revealed an overall decrease in the levels of Pol III-transcribed tRNAs and an imbalance in the levels of regulatory ncRNAs such as small nuclear and nucleolar RNAs (snRNAs and snoRNAs). In addition, the Pol III mutation was found to exert complex downstream effects on the Pol II transcriptome, affecting the general regulation of RNA metabolism.

Amyotrophic Lateral Sclerosis and Effects of Vibrations

Amyotrophic lateral sclerosis (ALS) is a severe and fatal neurodegenerative disorder affecting both the upper and lower motor neurons. We present the clinical cases of four patients with ALS and vibration syndrome. All patients had over 20 years of exposure to general and local vibrations and common subjective complaints: pain, paresthesia, twitching and weakness of limb muscles. Evidence of ALS syndrome was demonstrated by the abnormal neurological examination (pseudobulbar syndrome and pyramidal signs) as well as by neurophysiological studies (peripheral motor neuron degeneration). We discuss the possible relationship between the exposure to general and local vibrations and the ALS syndrome in our patients, and the role of vibrations as a possible risk factor for the disease. Occupational contact with chemicals and pesticides is also discussed as a risk factor.

Metabolic Disturbances In The Patients With Acute Ischemic Stroke

Summary The purpose of this study was to analyze the disturbances of glucose, lipid and protein metabolism in acute ischemic stroke patients. A total of 258 patients (mean age 70.9±7.22 years, range 49-92 years) were studied. The following parameters were examined: blood glucose, triglycerides, total cholesterol, HDL-cholesterol, LDL-cholesterol, creatinine, and urea. Data were statistically processed by variation and correlation analysis. Our results demonstrated abnormal values of these laboratory parameters in most patients. The mean concentrations of triglycerides, total cholesterol and LDL-cholesterol were higher in females, while these of blood glucose were higher in males, especially in the age group between 76 and 80 years. Pearson’s correlation coefficient was highest between the variables ‘total cholesterol’ and ‘LDL-cholesterol’ (r=0.797) but moderate - between some of the rest variables such as ‘creatinine’ and ‘urea’ (r=0.575); ‘total cholesterol’ and ‘triglycerides’ (r=0.565); ‘total cholesterol’ and ‘urea’ (r=0.428); ‘triglycerides’ and ‘urea’ (r=0.370) and ‘LDL-cholesterol’ and ‘urea’ (r=0.301). In conclusion, the metabolic disorders are relatively common among acute ischemic stroke patients and play a specific role as risk factors for this disease. These parameters should regularly be controlled within the outpatient practice in order to warrant an effective prevention of acute ischemic stroke.

Exome sequencing in roma families identifies tandem GRM1 mutations in a novel form of congenital cerebellar ataxia

&NA; Recessive ataxias are heterogeneous group of rare monogenic disorders with genetic pathology largely unresolved. Aim: To identify the molecular defect underlying a novel congenital ataxia phenotype in a small Roma sub-isolate with a known strong founder effect. Methods: The patients were assessed by an international multidisciplinary team. Whole exome sequencing data were used for inbreeding and relatedness estimates, linkage analysis and mutation detection. Functional mutation impact in patient lymphoblastoid cell lines was studied by reverse transcription/real-time PCR. Results: The major clinical manifestations included global developmental delay, gait and stance ataxia, intellectual deficit, and progressive cerebellar atrophy. Novel tandem deletion c.2652_2654del:p.884_885del and a splicing mutation c.2660+2T>G, 7 bp apart in the metabotropic glutamate receptor gene GRM1, were the only homozygous variants in all affected subjects both exome-wide and within a unique linkage region. The splicing defect had a major functional impact, with exon skipping or transcript termination in the neighboring intron producing various species of non-functional receptors either lacking the trans-membrane domain and containing abnormal intracellular tails or completely missing the tail. Discussion: The study is the first to implicate GRM1 in hereditary ataxia and to highlight the potential of exome sequencing in the Roma population for disease gene and mutation identification