Genetic landscape of early-onset dementia in Hungary.

INTRODUCTION: Early-onset dementias (EOD) are predominantly genetically determined, but the underlying disease-causing alterations are often unknown. The most frequent forms of EODs are early-onset Alzheimer's disease (EOAD) and frontotemporal dementia (FTD). PATIENTS: This study included 120 Hungarian patients with EOD (48 familial and 72 sporadic) which had a diagnosis of EOAD (n = 49), FTD (n = 49), or atypical dementia (n = 22). RESULTS: Monogenic dementia was detected in 15.8% of the patients. A pathogenic hexanucleotide repeat expansion in the C9ORF72 gene was present in 6.7% of cases and disease-causing variants were detected in other known AD or FTD genes in 6.7% of cases (APP, PSEN1, PSEN2, GRN). A compound heterozygous alteration of the TREM2 gene was identified in one patient and heterozygous damaging variants in the CSF1R and PRNP genes were detected in two other cases. In two patients, the coexistence of several heterozygous damaging rare variants associated with neurodegeneration was detected (1.7%). The APOE genotype had a high odds ratio for both the APOE ɛ4/3 and the ɛ4/4 genotype (OR = 2.7 (95%CI = 1.3-5.9) and OR = 6.5 (95%CI = 1.4-29.2), respectively). In TREM2, SORL1, and ABCA7 genes, 5 different rare damaging variants were detected as genetic risk factors. These alterations were not present in the control group. CONCLUSION: Based on our observations, a comprehensive, targeted panel of next-generation sequencing (NGS) testing investigating several neurodegeneration-associated genes may accelerate the path to achieve the proper genetic diagnosis since phenotypes are present on a spectrum. This can also reveal hidden correlations and overlaps in neurodegenerative diseases that would remain concealed in separated genetic testing.

The Role of the Rare Variants in the Genes Encoding the Alpha-Ketoglutarate Dehydrogenase in Alzheimer's Disease.

There is increasing evidence that several mitochondrial abnormalities are present in the brains of patients with Alzheimer's disease (AD). Decreased alpha-ketoglutarate dehydrogenase complex (αKGDHc) activity was identified in some patients with AD. The αKGDHc is a key enzyme in the Krebs cycle. This enzyme is very sensitive to the harmful effect of reactive oxygen species, which gives them a critical role in the Alzheimer and mitochondrial disease research area. Previously, several genetic risk factors were described in association with AD. Our aim was to analyze the associations of rare damaging variants in the genes encoding αKGDHc subunits and AD. The three genes (OGDH, DLST, DLD) encoding αKGDHc subunits were sequenced from different brain regions of 11 patients with histologically confirmed AD and the blood of further 35 AD patients. As a control group, we screened 134 persons with whole-exome sequencing. In all subunits, a one-one rare variant was identified with unknown significance based on American College of Medical Genetics and Genomics (ACMG) classification. Based on the literature research and our experience, R263H mutation in the DLD gene seems likely to be pathogenic. In the different cerebral areas, the αKGDHc mutational profile was the same, indicating the presence of germline variants. We hypothesize that the heterozygous missense R263H in the DLD gene may have a role in AD as a mild genetic risk factor.

Hereditary Parkinson's disease as a new clinical manifestation of the damaged POLG gene / [Az örökletes Parkinson-kór mint a POLG-gén károsodásának új klinikai megjelenési formája]

The protein product of the nuclear-encoded POLG gene plays a key role in the maintenance of mitochondrial DNA replication, and its failure causes multi-system diseases with varying severity. The clinical spectrum is extremely wide, and the most common symptoms include ptosis, myoclonus, epilepsy, myopathy, sensory ataxia, parkinsonism, cognitive decline and infertility. Now, it is known that mitochondrial dysfunction in Parkinson's disease plays a key role in the loss of dopaminergic neurons in the substantia nigra. Therefore, changes in the POLG gene may influence the development of various hereditary neurodegenerative diseases, including monogenic parkinsonism. However, only limited information is available on the relationship between Parkinson's disease and POLG gene and until now, there are no available data about the Hungarian population. In our study, we performed a next-generation sequencing study of 67 Hungarian patients with parkinsonism and analyzed the potentially damaging alterations in the POLG gene. 3 patients have been identified with a potential pathogen variant. In this study, we would like to call attention to the fact that during the differential diagnosis of parkinsonism, the possible involvement of POLG gene should be kept in mind. Especially in the presence of additional symptoms, such as ophthalmoparesis, non-vascular white matter lesions, psychiatric comorbidity, and relatively early age of onset, the POLG gene should be taken into consideration. Based on previous data from the literature and our own experience, we have summarized a possible diagnostic approach for POLG-associated parkinsonism. Orv Hetil. 2020; 161(20): 821-828.

Broadening the phenotype of the TWNK gene associated Perrault syndrome.

BACKGROUND: Perrault syndrome is a genetically heterogenous, very rare disease, characterized clinically by sensorineural hearing loss, ovarian dysfunction and neurological symptoms. We present the case of a 33 years old female patient with TWNK-associated Perrault syndrome. The TWNK gene is coding the mitochondrial protein Twinkle and currently there are only two reports characterizing the phenotype of TWNK-associated Perrault syndrome. None of these publications reported about special brain MRI alterations and neuropathological changes in the muscle and peripheral nerves. CASE PRESENTATION: Our patients with TWNK-dependent Perrault syndrome had severe bilateral hypoacusis, severe ataxia, polyneuropathy, lower limb spastic paraparesis with pyramidal signs, and gonadal dysgenesis. Psychiatric symptoms such as depression and paranoia were present as well. Brain MRI observed progressive cerebellar hyperintensive signs associated with cerebellar, medulla oblongata and cervical spinal cord atrophy. Light microscopy of the muscle biopsy detected severe neurogenic lesions. COX staining was centrally reduced in many muscle fibers. Both muscle and sural nerve electron microscopy detected slightly enlarged mitochondria with abnormal cristae surrounded by lipid vacuoles. In the sural nerve, dystrophic axons had focally uncompacted myelin lamellae present. Genetic investigation revealed multiple mtDNA deletion and compound heterozygous mutations of the TWNK gene (c.1196 A > G, c.1358 G > A). CONCLUSION: This study demonstrates that TWNK associated Perrault syndrome has a much broader phenotype as originally published. The coexistence of severe hypoacusis, spastic limb weakness, ataxia, polyneuropathy, gonadal dysgensia, hyperintense signals in the cerebellum and the presence of the mtDNA multiple deletion could indicate the impairment of the TWNK gene. This is the first report about pyramidal tract involvement and cerebellar MRI alteration associated with TWNK-related Perrault syndrome.

Comprehensive Analysis of Rare Variants of 101 Autism-Linked Genes in a Hungarian Cohort of Autism Spectrum Disorder Patients.

BACKGROUND: Autism spectrum disorder (ASD) is genetically and phenotypically heterogeneous. Former genetic studies suggested that both common and rare genetic variants play a role in the etiology. In this study, we aimed to analyze rare variants detected by next generation sequencing (NGS) in an autism cohort from Hungary. METHODS: We investigated the yield of NGS panel sequencing of an unselected ASD cohort (N = 174 ) for the detection of ASD associated syndromes. Besides, we analyzed rare variants in a common disease-rare variant framework and performed rare variant burden analysis and gene enrichment analysis in phenotype based clusters. RESULTS: We have diagnosed 13 molecularly proven syndromic autism cases. Strongest indicators of syndromic autism were intellectual disability, epilepsy or other neurological plus symptoms. Rare variant analysis on a cohort level confirmed the association of five genes with autism (AUTS2, NHS, NSD1, SLC9A9, and VPS13). We found no correlation between rare variant burden and number of minor malformation or autism severity. We identified four phenotypic clusters, but no specific gene was enriched in a given cluster. CONCLUSION: Our study indicates that NGS panel gene sequencing can be useful, where the clinical picture suggests a clinically defined syndromic autism. In this group, targeted panel sequencing may provide reasonable diagnostic yield. Unselected NGS panel screening in the clinic remains controversial, because of uncertain utility, and difficulties of the variant interpretation. However, the detected rare variants may still significantly influence autism risk and subphenotypes in a polygenic model, but to detect the effects of these variants larger cohorts are needed.

Whole mitochondrial genome diversity in two Hungarian populations.

Complete mitochondrial genomics is an effective tool for studying the demographic history of human populations, but there is still a deficit of mitogenomic data in European populations. In this paper, we present results of study of variability of 80 complete mitochondrial genomes in two Hungarian populations from eastern part of Hungary (Szeged and Debrecen areas). The genetic diversity of Hungarian mitogenomes is remarkably high, reaching 99.9% in a combined sample. According to the analysis of molecular variance (AMOVA), European populations showed a low, but statistically significant level of between-population differentiation (Fst = 0.61%, p = 0), and two Hungarian populations demonstrate lack of between-population differences. Phylogeographic analysis allowed us to identify 71 different mtDNA sub-clades in Hungarians, sixteen of which are novel. Analysis of ancestry-informative mtDNA sub-clades revealed a complex genetic structure associated with the genetic impact of populations from different parts of Eurasia, though the contribution from European populations is the most pronounced. At least 8% of ancestry-informative haplotypes found in Hungarians demonstrate similarity with East and West Slavic populations (sub-clades H1c23a, H2a1c1, J2b1a6, T2b25a1, U4a2e, K1c1j, and I1a1c), while the influence of Siberian populations is not so noticeable (sub-clades A12a, C4a1a, and probably U4b1a4).

Mitochondrial dysfunction and autism: comprehensive genetic analyses of children with autism and mtDNA deletion.

BACKGROUND: The etiology of autism spectrum disorders (ASD) is very heterogeneous. Mitochondrial dysfunction has been described in ASD; however, primary mitochondrial disease has been genetically proven in a small subset of patients. The main goal of the present study was to investigate correlations between mitochondrial DNA (mtDNA) changes and alterations of genes associated with mtDNA maintenance or ASD. METHODS: Sixty patients with ASD and sixty healthy individuals were screened for common mtDNA mutations. Next generation sequencing was performed on patients with major mtDNA deletions (mtdel-ASD) using two gene panels to investigate nuclear genes that are associated with ASD or are responsible for mtDNA maintenance. Cohorts of healthy controls, ASD patients without mtDNA alterations, and patients with mitochondrial disorders (non-ASD) harbouring mtDNA deletions served as comparison groups. RESULTS: MtDNA deletions were confirmed in 16.6% (10/60) of patients with ASD (mtdel-ASD). In 90% of this mtdel-ASD children we found rare SNVs in ASD-associated genes (one of those was pathogenic). In the intergenomic panel of this cohort one likely pathogenic variant was present. In patients with mitochondrial disease in genes responsible for mtDNA maintenance pathogenic mutations and variants of uncertain significance (VUS) were detected more frequently than those found in patients from the mtdel-ASD or other comparison groups. In healthy controls and in patients without a mtDNA deletion, only VUS were detected in both panel. CONCLUSIONS: MtDNA alterations are more common in patients with ASD than in control individuals. MtDNA deletions are not isolated genetic alterations found in ASD; they coexist either with other ASD-associated genetic risk factors or with alterations in genes responsible for intergenomic communication. These findings indicate that mitochondrial dysfunction is not rare in ASD. The occurring mtDNA deletions in ASD may be mostly a consequence of the alterations of the causative culprit genes for autism or genes responsible for mtDNA maintenance, or because of the harmful effect of environmental factors.

Targeted next generation sequencing of a panel of autism-related genes identifies an EHMT1 mutation in a Kleefstra syndrome patient with autism and normal intellectual performance.

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with unknown genetic and environmental causation in most of the affected individuals. On the other hand, there are a growing number of ASD-associated syndromes, where the exact genetic origin can be revealed. Here we report a method, which included the targeted next generation sequencing (NGS) and filtering of 101 ASD associated genes, followed by database search. Next, RNA sequencing was used to study the region of interest at the transcriptional level. Using this workflow, we identified a de novo mutation in the euchromatic histone-lysine N-methyltransferase 1 gene (EHMT1) of an autistic patient with dysmorphisms. Sequencing of EHMT1 transcripts showed that the premature termination codon (Trp1138Ter) created by a single nucleotide change elicited nonsense-mediated mRNA decay, which led to haploinsufficiency already at the transcriptional level. Database and literature search provided evidence that this mutation caused Kleefstra syndrome (KS), which was confirmed by the presence of the disorder-specific phenotype in the patient. We provide a proof of principle that the implemented method is capable to elucidate the genetic etiology of individuals with syndromic autism. The novel mutation detected in the EHMT1 gene is responsible for KS's symptoms. In addition, further genetic factors might be involved in the ASD pathogenesis of the patient including a missense DPP6 mutation (Arg322Cys), which segregated with the autistic phenotype within the family.

Genetic background of the hereditary spastic paraplegia phenotypes in Hungary - An analysis of 58 probands.

BACKGROUND: Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases with progressive lower limb spasticity and weakness. The aim of this study is to determine the frequency of different SPG mutations in Hungarian patients, and to provide further genotype-phenotype correlations for the known HSP causing genes. METHODS: We carried out genetic testing for 58 probands with clinical characteristics of HSP. For historical reasons, three different approaches were followed in different patients: 1) Sanger sequencing of ATL1 and SPAST genes, 2) whole exome, and 3) targeted panel sequencing by next generation sequencing. RESULTS: Genetic diagnosis was established for 20 probands (34.5%). We detected nine previously unreported mutations with high confidence for pathogenicity. The most frequently affected gene was SPAST with pathogenic or likely pathogenic mutations in 10 probands. The most frequently detected variant in our cohort was the SPG7 p.Leu78*, observed in four probands. Altogether five probands were diagnosed with SPG7. Additional mutations were detected in SPG11, ATL1, NIPA1, and ABCD1. CONCLUSION: This is the first comprehensive genetic epidemiological study of patients with HSP in Hungary. Next generation sequencing improved the yield of genetic diagnostics in this disease group even when the phenotype was atypical. However, considering the frequency of the HSP-causing gene defects, SPG4, the most common form of the disease, should be tested first to be cost effective in this economic region.

Asian-specific mitochondrial genome polymorphism (9-bp deletion) in Hungarian patients with mitochondrial disease.

A 9-bp deletion of the mtDNA is known as an anthropological marker of people with East-Asian origin. This 9-bp mtDNA deletion was analyzed in 1073 Hungarians with suspected mitochondrial disease and in 468 healthy control individuals. Fourteen cases with the 9-bp deletion were found in the cohort of mitochondrial patients, and one individual from 468 controls. In six cases the 9-bp deletion was present together with pathogenic major deletions in the mitochondrial genome. In one patient we found a frame shift mutation in the D-loop region, and in another family a pathogenic m.8322 A > G mutation in the tRNA(Lys) gene. Although the 9-bp deletion is common in the populations of the Pacific region and Asia, it is present in the Hungarian population as well. This 9-bp deletion may induce instability of the mtDNA and may provoke the introduction of other pathogenic mutations.

Retrospective assessment of the most common mitochondrial DNA mutations in a large Hungarian cohort of suspect mitochondrial cases.

Prevalence estimations for mitochondrial disorders still vary widely and only few epidemiologic studies have been carried out so far. With the present work we aim to give a comprehensive overview about frequencies of the most common mitochondrial mutations in Hungarian patients. A total of 1328 patients were tested between 1999 and 2012. Among them, 882 were screened for the m.3243A > G, m.8344A > G, m.8993T > C/G mutations and deletions, 446 for LHON primary mutations. The mutation frequency in our cohort was 2.61% for the m.3243A > G, 1.47% for the m.8344A > G, 17.94% for Leber's Hereditary Optic Neuropathy (m.3460G > A, m.11778G > A, m.14484T > C) and 0.45% for the m.8993T > C/G substitutions. Single mtDNA deletions were detected in 14.97%, while multiple deletions in 6.01% of the cases. The mutation frequency in Hungarian patients suggestive of mitochondrial disease was similar to other Caucasian populations. Further retrospective studies of different populations are needed in order to accurately assess the importance of mitochondrial diseases and manage these patients.

Coexisting huntingtin and SCA8 repeat expansion: case report of a severe complex neurodegenerative syndrome.

We report the case of a 29 year old woman with a complex movement disorder syndrome due to the combination of coexisting pathological triplet repeat expansions of huntingtin and ATXN8 genes. The disease course was characterized by mental disturbances including cognitive decline and changes in personality starting at the age of 12 years, followed by twisting motions, intentional tremor and gait ataxia. Later Parkinsonian symptoms of micrographia, bradykinesia, muscle rigidity and mental decline became dominant. Brain MRI showed hypoplasia of the nucleus caudatus and generalized atrophy; MR spectroscopy revealed a decrease of all typical metabolites except for an increased level of lactate and acetate. Therapeutic trials with pramipexole, ropinirole and tetrabenazine showed no benefit, while levetiracetam caused agitation and hallucinations. We discuss phenotype-genotype correlation and the rule of triplet repeat expansions of gene ATXN8.

Bcl-2 or bcl-XL gene therapy increases neural plasticity proteins nestin and c-fos expression in PC12 cells.

The anti-apoptotic gene replacements could be an option in preventing hypoxia-induced neuronal loss. In this paper we tested the effect of anti-apoptosis (bcl-2 and bcl-XL) gene transfer on cell plasticity. Nestin, synapsin-1 and c-fos genes and proteins expression were measured in PC12 cells in normal condition, and after hypoxia/re-oxygenation. Gene delivery results a significant increase in both bcl-2 and bcl-XL gene expression. Hypoxia (1h)/re-oxygenation (24h) have a detrimental effect upon cultured cells by increasing the pro-apoptotic, bax gene and protein expression. Bcl-2 or bcl-XL gene delivery resulted in a significant increase in and the cellular levels of the corresponding mRNAs and proteins. Bcl-2 gene augmented the nestin gene and protein expression which has been compromised previously by the hypoxic event. Similarly c-fos mRNA and protein expression decreased significantly after hypoxia, while the anti-apoptotic gene treatment normalized c-fos expression. Synapsin-1 gene or protein expression remained about on the same level under normoxic conditions or following hypoxia after gene treatment. We can conclude that anti-apoptotic gene transfers activate neuronal plasticity proteins nestin and c-fos. This link on anti-apoptotic proteins and cell plasticity is a new finding.

[Maternally inherited diabetes mellitus, deafness, chronic progressive external ophthalmoplegia and myopathy as the result of A3243G mutation of mtDNA]. / Maternalisan öröklôdô diabetes mellitus, nagyothallás, kronikus progressziv ophthalmoplegia externa es myopathia mint az MTDNS A3243G-mutáció következménye.

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome are caused mainly by the A3243G mutation of the mitochondrial genome. The A3243G substitution of mitochondrial DNA (mtDNA) is also responsible for various, other clinical phenotypes and syndromes. Here we report the case of a 33-year-old woman, with childhood onset ophthalmoplegia externa, progressive, generalised exercise intolerability, muscle weakness, hypacusis and diabetes mellitus as the symptoms of mitochondrial disease. Genetic analysis of the mitochondrial DNA revealed a heteroplasmic A to G substitution at position 3243 in the tRNS Leu(UUR) gene. In our case the classical MELAS phenotype has not yet appeared, however, some examples show in the literature that maternally inherited diabetes mellitus, progressive hypacusis, progressive ophthalmoplegia externa, exercise intolerance, and myopathy are often linked to as isolated symptoms of A3243G mutation. The phenotype in the family is consistent, the proband's daughter has ptosis, exercise intolerance, and myopathy, too. A brief summary of the different clinical phenotypes associated with A3243G mutation, and of the different mtDNA mutations which can cause chronic progressive ophthalmoplegia externa (CPEO) will also be reviewed in this case report.