TREX1 p.A129fs and p.Y305C variants in a large multi-ethnic cohort of CADASIL-like unrelated patients.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and retinal vasculopathy with cerebral leukodystrophy and systemic manifestations (RVCL-S) are the most common forms of rare monogenic early-onset cerebral small vessel disease and share clinical, and, to different extents, neuroradiological and neuropathological features. However, whether CADASIL and RVCL-S overlapping phenotype may be explained by shared genetic risk or causative factors such as TREX1 coding variants remains poorly understood. To investigate this intriguing hypothesis, we used exome sequencing to screen TREX1 protein-coding variability in a large multi-ethnic cohort of 180 early-onset independent familial and apparently sporadic CADASIL-like Caucasian patients from the USA, Portugal, Finland, Serbia and Turkey. We report 2 very rare and likely pathogenic TREX1 mutations: a loss of function mutation (p.Ala129fs) clustering in the catalytic domain, in an apparently sporadic 46-year-old patient from the USA and a missense mutation (p.Tyr305Cys) in the well conserved C-terminal region, in a 57-year-old patient with positive family history from Serbia. In concert with recent findings, our study expands the clinical spectrum of diseases associated with TREX1 mutations.

Clinical features and spectrum of NOTCH3 variants in Finnish patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

OBJECTIVES: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a cerebral small vessel disease caused by pathogenic variants in the NOTCH3 gene. In Finland, the majority of CADASIL patients carry the pathogenic founder variant c.397C>T, (p.Arg133Cys), but the spectrum of other NOTCH3 variants has not been investigated previously. The aim of the study was to investigate the spectrum and prevalence of NOTCH3 variants Finnish CADASIL patients and to examine the clinical features associated with them. MATERIALS AND METHODS: The spectrum of NOTCH3 variants and the clinical features associated with them were retrospectively examined in 294 Finnish CADASIL patients tested during January 1996 to October 2021 in the Medical Genetics laboratory of Department of Genomics of Turku University Hospital, where practically all samples of patients with suspected CADASIL in Finland are investigated. RESULTS: The most common NOTCH3 variants in the study cohort were c.397C>T, (p.Arg133Cys) (68%) and c.3206A>G p.(Tyr1069Cys) (18%), but other less common NOTCH3 variants were detected in as many as 14% of the patients. Eight of the detected NOTCH3 variants were novel: c.520T>A,p.(Cys174Ser), c.836A>G,p.(Gln279Arg), c.1369T>G,p.(Cys457Gly), c.1338C>G,p.(Cys446Trp), c.1564T>G,p.(Cys522Gly), c.2848T>G,p.(Cys950Gly), c.6102dup,p.(Gly2035Argfs*60), and c.2410+6C>G. Other NOTCH3 variants than p.Arg133Cys and p.Tyr1069Cys were more often associated with more severe clinical features. CONCLUSION: This study revealed the genetic and clinical spectrum of CADASIL in the Finnish population. Sequencing of the whole NOTCH3 gene performing a gene-panel or exome sequencing is recommended when suspecting CADASIL.

Genetic analysis reveals novel variants for vascular cognitive impairment.

OBJECTIVES: The genetic background of vascular cognitive impairment (VCI) is poorly understood compared to other dementia disorders. The aim of the study was to investigate the genetic background of VCI in a well-characterized Finnish cohort. MATERIALS & METHODS: Whole-exome sequencing (WES) was applied in 45 Finnish VCI patients. Copy-number variant (CNV) analysis using a SNP array was performed in 80 VCI patients. This study also examined the prevalence of variants at the miR-29 binding site of COL4A1 in 73 Finnish VCI patients. RESULTS: In 40% (18/45) of the cases, WES detected possibly causative variants in genes associated with cerebral small vessel disease (CSVD) or other neurological or stroke-related disorders. These variants included HTRA1:c.847G>A p.(Gly283Arg), TREX1:c.1079A>G, p.(Tyr360Cys), COLGALT1:c.1411C>T, p.(Arg471Trp), PRNP: c.713C>T, p.(Pro238Leu), and MTHFR:c.1061G>C, p.(Gly354Ala). Additionally, screening of variants in the 3'UTR of COL4A1 gene in a sub-cohort of 73 VCI patients identified a novel variant c.*36T>A. CNV analysis showed that pathogenic CNVs are uncommon in VCI. CONCLUSIONS: These data support pathogenic roles of variants in HTRA1, TREX1 and in the 3'UTR of COL4A1 in CSVD and VCI, and suggest that vascular pathogenic mechanisms are linked to neurodegeneration, expanding the understanding of the genetic background of VCI.

PHACTR1 genetic variability is not critical in small vessel ischemic disease patients and PcomA recruitment in C57BL/6J mice.

Recently, several genome-wide association studies identified PHACTR1 as key locus for five diverse vascular disorders: coronary artery disease, migraine, fibromuscular dysplasia, cervical artery dissection and hypertension. Although these represent significant risk factors or comorbidities for ischemic stroke, PHACTR1 role in brain small vessel ischemic disease and ischemic stroke most important survival mechanism, such as the recruitment of brain collateral arteries like posterior communicating arteries (PcomAs), remains unknown. Therefore, we applied exome and genome sequencing in a multi-ethnic cohort of 180 early-onset independent familial and apparently sporadic brain small vessel ischemic disease and CADASIL-like Caucasian patients from US, Portugal, Finland, Serbia and Turkey and in 2 C57BL/6J stroke mouse models (bilateral common carotid artery stenosis [BCCAS] and middle cerebral artery occlusion [MCAO]), characterized by different degrees of PcomAs patency. We report 3 very rare coding variants in the small vessel ischemic disease-CADASIL-like cohort (p.Glu198Gln, p.Arg204Gly, p.Val251Leu) and a stop-gain mutation (p.Gln273*) in one MCAO mouse. These coding variants do not cluster in PHACTR1 known pathogenic domains and are not likely to play a critical role in small vessel ischemic disease or brain collateral circulation. We also exclude the possibility that copy number variants (CNVs) or a variant enrichment in Phactr1 may be associated with PcomA recruitment in BCCAS mice or linked to diverse vascular traits (cerebral blood flow pre-surgery, PcomA size, leptomeningeal microcollateral length and junction density during brain hypoperfusion) in C57BL/6J mice, respectively. Genetic variability in PHACTR1 is not likely to be a common susceptibility factor influencing small vessel ischemic disease in patients and PcomA recruitment in C57BL/6J mice. Nonetheless, rare variants in PHACTR1 RPEL domains may influence the stroke outcome and are worth investigating in a larger cohort of small vessel ischemic disease patients, different ischemic stroke subtypes and with functional studies.

Whole-exome sequencing of Finnish patients with vascular cognitive impairment.

Cerebral small vessel disease (CSVD) is the most important cause of vascular cognitive impairment (VCI). Most CSVD cases are sporadic but familial monogenic forms of the disorder have also been described. Despite the variants identified, many CSVD cases remain unexplained genetically. We used whole-exome sequencing in an attempt to identify novel gene variants underlying CSVD. A cohort of 35 Finnish patients with suspected CSVD was analyzed. Patients were screened negative for the most common variants affecting function in NOTCH3 in Finland (p.Arg133Cys and p.Arg182Cys). Whole-exome sequencing was performed to search for a genetic cause of CSVD. Our study resulted in the detection of possibly pathogenic variants or variants of unknown significance in genes known to associate with CSVD in six patients, accounting for 17% of cases. Those genes included NOTCH3, HTRA1, COL4A1, and COL4A2. We also identified variants with predicted pathogenic effect in genes associated with other neurological or stroke-related conditions in seven patients, accounting for 20% of cases. This study supports pathogenic roles of variants in COL4A1, COL4A2, and HTRA1 in CSVD and VCI. Our results also suggest that vascular pathogenic mechanisms are linked to neurodegenerative conditions and provide novel insights into the molecular basis of VCI.

Oligogenic basis of sporadic ALS: The example of SOD1 p.Ala90Val mutation.

OBJECTIVE: To characterize the clinical and neuropathologic features of patients with amyotrophic lateral sclerosis (ALS) with the superoxide dismutase 1 (SOD1) p.Ala90Val mutation, as well as the mutation frequency and the role of oligogenic mechanisms in disease penetrance. METHODS: An index patient with autopsy-proven ALS was discovered to have the SOD1 p.Ala90Val mutation, which was screened in 2 Finnish ALS cohorts (n = 453). Additional contributing variants were analyzed from whole-genome or whole-exome sequencing data. RESULTS: Seven screened patients (1.5%) were found to carry the SOD1 heterozygous mutation. Allele-sharing analysis suggested a common founder haplotype. Common clinical features included limb-onset, long disease course, and sensory symptoms. No TDP43 pathology was observed. All cases were apparently sporadic, and pedigree analysis demonstrated that the mutation has reduced penetrance. Analysis of other contributing genes revealed a unique set of additional variants in each patient. These included previously described rare ANG and SPG11 mutations. One patient was compound heterozygous for SOD1 p.Ala90Val and p.Asp91Ala. CONCLUSIONS: Our data suggest that the penetrance of SOD1 p.Ala90Val is modulated by other genes and indicates highly individual oligogenic basis of apparently sporadic ALS. Additional genetic variants likely contributing to disease penetrance were very heterogeneous, even among Finnish patients carrying the SOD1 founder mutation.

A founder mutation in CERKL is a major cause of retinal dystrophy in Finland.

PURPOSE: To study the genetic aetiology of retinal dystrophies (RD) in Finnish patients. METHODS: A targeted next-generation sequencing (NGS) panel of 105 retinal dystrophy genes was used in a cohort of 55 RD patients. RESULTS: The overall diagnostic yield was 60% demonstrating the power of this approach. Interestingly, a missense mutation c.375C>G p.(Cys125Trp) in the CERKL gene was found in 18% of the patients in either a homozygous or compound heterozygous state. Data from Exome Aggregation Consortium (ExAC) Browser show that the CERKL c.375C>G p.(Cys125Trp) allele is enriched in the Finnish population and thus is a founder mutation. Furthermore, we report the clinical picture of 18 patients with mutations in the CERKL gene. CERKL mutations cause a macular-onset disease, in which symptoms first become apparent at the second decade. We also detected other novel founder mutations in the CERKL, EYS, RP1, ABCA4 and GUCY2D genes. CONCLUSION: Our report indicates that the first diagnostic test for Finnish patients with sporadic or autosomal recessive RD should be a targeted test for founder mutations in the CERKL, EYS, RP1, ABCA4 and GUCY2D genes. These results confirm the utility of NGS-based gene panels as a powerful method for mutation identification in RD, thus enabling improved genetic counselling for these families.

A Novel Loss-of-Function GRN Mutation p.(Tyr229*): Clinical and Neuropathological Features.

Mutations in the progranulin (GRN) gene represent about 5-10% of frontotemporal lobar degeneration (FTLD). We describe a proband with a novel GRN mutation c.687T>A, p.(Tyr229*), presenting with dyspraxia, dysgraphia, and dysphasia at the age of 60 and a very severe FTLD neuropathological phenotype with TDP43 inclusions. The nephew of the proband had signs of dementia and personality changes at the age of 60 and showed similar but milder FTLD pathology. Three other family members had had early-onset dementia. Gene expression studies showed decreased GRN gene expression in mutation carriers' blood samples. In conclusion, we describe a novel GRN, p.(Tyr229*) mutation, resulting in haploinsufficiency of GRN and a severe neuropathologic FTLD phenotype.