RFC1 and FGF14 Repeat Expansions in Serbian Patients with Cerebellar Ataxia.

BACKGROUND: The newly discovered intronic repeat expansions in the genes encoding replication factor C subunit 1 (RFC1) and fibroblast growth factor 14 (FGF14) frequently cause late-onset cerebellar ataxia. OBJECTIVES: To investigate the presence of RFC1 and FGF14 pathogenic repeat expansions in Serbian patients with adult-onset cerebellar ataxia. METHODS: The study included 167 unrelated patients with sporadic or familial cerebellar ataxia. The RFC1 repeat expansion analysis was performed by duplex PCR and Sanger sequencing, while the FGF14 repeat expansion was tested for by long-range PCR, repeat-primed PCR, and Sanger sequencing. RESULTS: We identified pathogenic repeat expansions in RFC1 in seven patients (7/167; 4.2%) with late-onset sporadic ataxia with neuropathy and chronic cough. Two patients also had bilateral vestibulopathy. Repeat expansions in FGF14 were found in nine unrelated patients (9/167; 5.4%) with ataxia, less than half of whom presented with neuropathy and two-thirds with global brain atrophy. Tremor and episodic features were the most frequent additional characteristics in carriers of uninterrupted FGF14 repeat expansions. Among the 122 sporadic cases, 12 (9.8%) carried an expansion in either RFC1 or FGF14, comparable to 4/45 (8.9%) among the patients with a positive family history. CONCLUSIONS: Pathogenic repeat expansions in RFC1 and FGF14 are relatively frequent causes of adult-onset cerebellar ataxia, especially among sporadic patients, indicating that family history should not be considered when prioritizing ataxia patients for testing of RFC1 or FGF14 repeat expansions.

Large-Scale Screening: Phenotypic and Mutational Spectrum in Isolated and Combined Dystonia Genes.

BACKGROUND: Pathogenic variants in several genes have been linked to genetic forms of isolated or combined dystonia. The phenotypic and genetic spectrum and the frequency of pathogenic variants in these genes have not yet been fully elucidated, neither in patients with dystonia nor with other, sometimes co-occurring movement disorders such as Parkinson's disease (PD). OBJECTIVES: To screen >2000 patients with dystonia or PD for rare variants in known dystonia-causing genes. METHODS: We screened 1207 dystonia patients from Germany (DysTract consortium), Spain, and South Korea, and 1036 PD patients from Germany for pathogenic variants using a next-generation sequencing gene panel. The impact on DNA methylation of KMT2B variants was evaluated by analyzing the gene's characteristic episignature. RESULTS: We identified 171 carriers (109 with dystonia [9.0%]; 62 with PD [6.0%]) of 131 rare variants (minor allele frequency <0.005). A total of 52 patients (48 dystonia [4.0%]; four PD [0.4%, all with GCH1 variants]) carried 33 different (likely) pathogenic variants, of which 17 were not previously reported. Pathogenic biallelic variants in PRKRA were not found. Episignature analysis of 48 KMT2B variants revealed that only two of these should be considered (likely) pathogenic. CONCLUSION: This study confirms pathogenic variants in GCH1, GNAL, KMT2B, SGCE, THAP1, and TOR1A as relevant causes in dystonia and expands the mutational spectrum. Of note, likely pathogenic variants only in GCH1 were also found among PD patients. For DYT-KMT2B, the recently described episignature served as a reliable readout to determine the functional effect of newly identified variants. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Discordant Monozygotic Parkinson Disease Twins: Role of Mitochondrial Integrity.

OBJECTIVE: Even though genetic predisposition has proven to be an important element in Parkinson's disease (PD) etiology, monozygotic (MZ) twins with PD displayed a concordance rate of only about 20% despite their shared identical genetic background. METHODS: We recruited 5 pairs of MZ twins discordant for idiopathic PD and established skin fibroblast cultures to investigate mitochondrial phenotypes in these cellular models against the background of a presumably identical genome. To test for genetic differences, we performed whole genome sequencing, deep mitochondrial DNA (mtDNA) sequencing, and tested for mitochondrial deletions by multiplex real-time polymerase chain reaction (PCR) in the fibroblast cultures. Further, the fibroblast cultures were tested for mitochondrial integrity by immunocytochemistry, immunoblotting, flow cytometry, and real-time PCR to quantify gene expression. RESULTS: Genome sequencing did not identify any genetic difference. We found decreased mitochondrial functionality with reduced cellular adenosine triphosphate (ATP) levels, altered mitochondrial morphology, elevated protein levels of superoxide dismutase 2 (SOD2), and increased levels of peroxisome proliferator-activated receptor-gamma coactivator-α (PPARGC1A) messenger RNA (mRNA) in skin fibroblast cultures from the affected compared to the unaffected twins. Further, there was a tendency for a higher number of somatic mtDNA variants among the affected twins. INTERPRETATION: We demonstrate disease-related differences in mitochondrial integrity in the genetically identical twins. Of note, the clinical expression matches functional alterations of the mitochondria. ANN NEUROL 2021;89:158-164.

De Novo Variants in TAOK1 Cause Neurodevelopmental Disorders.

De novo variants represent a significant cause of neurodevelopmental delay and intellectual disability. A genetic basis can be identified in only half of individuals who have neurodevelopmental disorders (NDDs); this indicates that additional causes need to be elucidated. We compared the frequency of de novo variants in patient-parent trios with (n = 2,030) versus without (n = 2,755) NDDs. We identified de novo variants in TAOK1 (thousand and one [TAO] amino acid kinase 1), which encodes the serine/threonine-protein kinase TAO1, in three individuals with NDDs but not in persons who did not have NDDs. Through further screening and the use of GeneMatcher, five additional individuals with NDDs were found to have de novo variants. All eight variants were absent from gnomAD (Genome Aggregation Database). The variant carriers shared a non-specific phenotype of developmental delay, and six individuals had additional muscular hypotonia. We established a fibroblast line of one mutation carrier, and we demonstrated that reduced mRNA levels of TAOK1 could be increased upon cycloheximide treatment. These results indicate nonsense-mediated mRNA decay. Further, there was neither detectable phosphorylated TAO1 kinase nor phosphorylated tau in these cells, and mitochondrial morphology was altered. Knockdown of the ortholog gene Tao1 (Tao, CG14217) in Drosophila resulted in delayed early development. The majority of the Tao1-knockdown flies did not survive beyond the third instar larval stage. When compared to control flies, Tao1 knockdown flies revealed changed morphology of the ventral nerve cord and the neuromuscular junctions as well as a decreased number of endings (boutons). Furthermore, mitochondria in mutant flies showed altered distribution and decreased size in axons of motor neurons. Thus, we provide compelling evidence that de novo variants in TAOK1 cause NDDs.

Association of SNCA variants with α-synuclein of gastric and colonic mucosa in Parkinson's disease.

BACKGROUND: Alpha-synuclein (α-Syn) immunostaining in the enteric nervous system (ENS) has been investigated to determine the role of diagnostic biomarker of Parkinson's disease (PD). However, determining factors for alpha-synuclein (α-Syn) deposition in the ENS of humans are still unclear. We aimed to investigate a possible association between SNCA variants and the presence of α-Syn immunostaining in the ENS in patients with PD and healthy individuals. METHODS: The study subjects consisted of 38 patients with PD and 46 healthy individuals. α-Syn immunohistochemistry was performed for gastric and colonic mucosal tissues of patients with PD and controls. Mucosal biopsy tissues of the ENS were obtained using standard biopsy forceps by endoscopic gastroduodenoscopy or colonoscopy. Two variants within the SNCA gene (the single nucleotide polymorphism [SNP] rs11931074 and the microsatellite REP1) were genotyped. RESULTS: In patients with PD, the rs11931074 (G allele) was significantly associated with the presence of α-Syn immunostaining in the ENS (OR = 5.96, 95% CI = 1.70-20.97, P = 0.01). In an interaction analysis, SNP rs11931074-PD status interaction was significantly associated with positive α-Syn immunostaining in the ENS (OR = 7.33, 95% CI = 1.58-33.88, P = 0.01). Longer SNCA REP1 alleles were not associated with positive α-Syn immunostaining in the ENS. CONCLUSION: This exploratory study demonstrated that α-Syn deposition in the ENS may be associated with SNCA variants in patients with PD.

Novel homozygous variants in ATCAY, MCOLN1, and SACS in complex neurological disorders.

BACKGROUND: Neurological disorders comprise a large group of clinically and genetically heterogeneous disorders, many of which have a genetic cause. In addition to a detailed neurological examination, exome sequencing is being increasingly used as a complementary diagnostic tool to identify the underlying genetic cause in patients with unclear, supposedly genetically determined disorders. OBJECTIVE: To identify the genetic cause of a complex movement disorder in five consanguineous Pakistani families. METHODS: We included five consanguineous Pakistani families with complex recessively inherited movement disorders. Clinical investigation including videotaping was carried out in a total of 59 family members (4-21 per family) and MRI in six patients. Exome sequencing was performed in 4-5 family members per pedigree to explore the underlying genetic cause. RESULTS: Patients presented a wide spectrum of neurological symptoms including ataxia and/or dystonia. We identified three novel homozygous, segregating variants in ATCAY (p.Pro200Profs*20), MCOLN1 (p.Ile184Thr), and SACS (p.Asn3040Lysfs*4) in three of the families. Thus, we were able to identify the likely cause of the disease in a considerable number of families (60%) with the relatively simple and nowadays widely available method of exome sequencing. Of note, close collaboration of neurologists and geneticists was instrumental for proper data interpretation. CONCLUSIONS: We expand the phenotypic, genotypic, and ethnical spectrum of mutations in these genes. Our findings alert neurologists that rare genetic causes should be considered in complex phenotypes regardless of ethnicity.

Complex and Dynamic Chromosomal Rearrangements in a Family With Seemingly Non-Mendelian Inheritance of Dopa-Responsive Dystonia.

Importance: Chromosomal rearrangements are increasingly recognized to underlie neurologic disorders and are often accompanied by additional clinical signs beyond the gene-specific phenotypic spectrum. Objective: To elucidate the causal genetic variant in a large US family with co-occurrence of dopa-responsive dystonia as well as skeletal and eye abnormalities (ie, ptosis, myopia, and retina detachment). Design, Setting, and Participants: We examined 10 members of a family, including 5 patients with dopa-responsive dystonia and skeletal and/or eye abnormalities, from a US tertiary referral center for neurological diseases using multiple conventional molecular methods, including fluorescence in situ hybridization and array comparative genomic hybridization as well as large-insert whole-genome sequencing to survey multiple classes of genomic variations. Of note, there was a seemingly implausible transmission pattern in this family due to a mutation-negative obligate mutation carrier. Main Outcomes and Measures: Genetic diagnosis in affected family members and insight into the formation of large deletions. Results: Four members were diagnosed with definite and 1 with probable dopa-responsive dystonia. All 5 affected individuals carried a large heterozygous deletion encompassing all 6 exons of GCH1. Additionally, all mutation carriers had congenital ptosis requiring surgery, 4 had myopia, 2 had retinal detachment, and 2 showed skeletal abnormalities of the hands, ie, polydactyly or syndactyly or missing a hand digit. Two individuals were reported to be free of any disease. Analyses revealed complex chromosomal rearrangements on chromosome 14q21-22 in unaffected individuals that triggered the expansion to a larger deletion segregating with affection status. The expansion occurred recurrently, explaining the seemingly non-mendelian inheritance pattern. These rearrangements included a deletion of GCH1, which likely contributes to the dopa-responsive dystonia, as well as a deletion of BMP4 as a potential cause of digital and eye abnormalities. Conclusions and Relevance: Our findings alert neurologists to the importance of clinical red flags, ie, unexpected co-occurrence of clinical features that may point to the presence of chromosomal rearrangements as the primary disease cause. The clinical management and diagnostics of such patients requires an interdisciplinary approach in modern clinical-diagnostic care.

The role of mutations in COL6A3 in isolated dystonia.

Specific mutations in COL6A3 have recently been reported as the cause of isolated recessive dystonia, which is a rare movement disorder. In all patients, at least one mutation was located in Exons 41 and 42. In an attempt to replicate these findings, we assessed by direct sequencing the frequency of rare variants in Exons 41 and 42 of COL6A3 in 955 patients with isolated or combined dystonia or with another movement disorder with dystonic features. We identified nine heterozygous carriers of rare variants including five different missense mutations and an extremely rare synonymous variant. In these nine patients, we sequenced the remaining 41 coding exons of COL6A3 to test for a second mutation in the compound heterozygous state. In only one of them, a second rare variant was identified (Thr732Met + Pro3082Arg). Of note, this patient had been diagnosed with Parkinson´s disease (with dystonic posturing) due to homozygous PINK1 mutations. The COL6A3 mutations clearly did not segregate with the disease in the four affected siblings of this family. Further, there was no indication for a disease-modifying effect of the COL6A3 mutations since disease severity or age at onset did not correlate with the number of COL6A3 mutated alleles in this family. In conjunction with the relatively high frequency of homozygous carriers of reported mutations in publically available databases, our data call a causal role for variants in COL6A3 in isolated dystonia into question.

A de novo unbalanced translocation leading to partial monosomy 9p23-pter and partial trisomy 15q25.3-qter associated with 46,XY complete gonadal dysgenesis, tall stature and mental retardation.

Syndromic forms of disorders of sex development constitute a challenge for clinical and molecular investigations. We report on a 12-year-old girl presenting with lack of pubertal development, tall stature and moderate mental retardation. Conventional karyotyping at the age of 3 years revealed a male karyotype (46,XY). At the age of 12 years, the girl had no signs of puberty, and laboratory values were consistent with hypergonadotropic hypogonadism because of complete gonadal dysgenesis. Histology at the time of gonadectomy revealed fibrous tissue without testicular morphology. Cytogenetic reevaluation at that time showed additional material of unknown origin on the short arm of chromosome 9. Subsequent fluorescence in-situ hybridization and Array-CGH analyses revealed an unbalanced translocation between 9p and 15q resulting in a partial monosomy of 9p and a partial trisomy of 15q. The karyotype was described as 46,XY,der(9)t(9;15)(p23;q25.3). We discuss the clinical and molecular cytogenetic findings with respect to the literature.

Validation of primed in situ labeling for interphase analysis of chromosomes 18, X, and Y in uncultured amniocytes.

OBJECTIVE: Primed in situ labeling (PRINS) is an interesting alternative to the traditional fluorescence in situ hybridization (FISH) for the in situ detection of specific sequences in chromosome anomalies. It combines the sensitivity and specificity of the polymerase chain reaction with the specific in situ signal detection capability of FISH. METHODS: We performed PRINS on uncultured amniocytes and compared the results with standard cytogenetic analysis. In a prospective study, a total of 262 independent samples were analyzed for numerical aberrations of chromosome 18. RESULTS: In more than 95% of the cases PRINS reactions were successfully achieved. Neither false-positive nor false-negative results were obtained. 62 of the 262 cases were in parallel examined for chromosome 18 aneuploidies by FISH. Although there were significant differences in signal distribution, these did not lead to a different overall classification of the respective cases, i.e., the end results of disomic and trisomic cases for chromosome 18 were identical between FISH and PRINS. In 205 of 262 cases PRINS was performed for chromosomes X and Y. 97.6% of these samples were properly sex differentiated. CONCLUSIONS: The PRINS assay is a simple and cheap alternative to detect numerical aberrations of chromosome 18. However, the rate of false-positive results for chromosome X was calculated as 1% and the rate of false-negative ones for chromosome Y as 2%. Further investigations are required to transform PRINS into an alternative to conventional methods for routine rapid prenatal diagnosis of gonosomes.