Ivana Novaković

Background/Objectives: Early-onset dementia (EOD), defined as symptom onset before 65 years of age, is a clinically and genetically heterogeneous group. Alzheimer’s disease (AD) and frontotemporal dementia (FTD) are its most common neurodegenerative causes. Methods: We investigated the family history, genetic spectrum, and diagnostic yield of targeted genetic testing in a consecutive Serbian cohort of 130 patients with early-onset AD (EOAD) and 78 with early-onset FTD (EOFTD). Results: Approximately one-third of patients had a positive family history of dementia or another neurodegenerative disorder. Pathogenic or likely pathogenic variants were identified in 3.8% of patients with EOAD, whereas pathogenic or likely pathogenic variants or pathogenic repeat expansions were identified in 9.0% of patients with EOFTD. In EOAD, the diagnostic yield increased to 9.5% in those with a positive family history and, in an exploratory subgroup analysis, was 33.3% in those with symptom onset before 51 years. In EOFTD, the diagnostic yield was 25.0% among those with a positive family history. PSEN1 and APP were the only disease-causing genes identified in EOAD, whereas C9orf72 repeat expansion was the predominant genetic cause of EOFTD, with additional pathogenic variants identified in GRN and VCP. Conclusions: These findings support the clinical value of targeted genetic testing guided by family history, age at onset, and clinical phenotype in patients with EOD. Genetically unresolved familial cases may reflect incomplete assessment of known genetic causes, including genes and variant classes not covered by the targeted testing strategy used in this study.

Introduction: Parkinson’s disease (PD) is a prevalent neurodegenerative disorder, with several proposed pathogenic mechanisms. Given the established role of mitochondrial dysfunction in PD, this study seeks to investigate the enrichment of rare genetic variants tied to mitochondrial metabolism in cases of early-onset and familial PD. Methods: We performed a retrospective analysis on 248 early-onset and familial PD patients and 1622 control individuals. We assessed both pathway-level and gene-level burden of germline rare variants detected using exome sequencing in 467 nuclear genes related to mitochondrial metabolism. Results: Gene-set mutation burden analysis indicated an increased burden in genes associated with mtDNA maintenance. In addition, gene-level analysis identified a possible association between PD and rare variant burden in 14 mitochondrial metabolism-related genes under dominant or recessive inheritance models. Conclusions: Our findings support a potential contribution of rare germline variants affecting mitochondrial metabolism to the susceptibility in early-onset and familial PD.

Background: Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are recognized as a spectrum of neurodegenerative disorders with overlapping clinical, pathological, and genetic features. The identification of C9orf72 hexanucleotide repeat expansion as the most common genetic cause of both conditions has prompted further investigation of genetic modifiers that may contribute to disease heterogeneity. We aimed to analyze the frequency of C9orf72 repeat expansions and potential modifying roles of APOE, ATXN1, and ATXN2 in Serbian ALS/FTD patients. Methods: Our study included an ALS/FTD cohort (n = 22) and healthy controls (n = 94). Repeat sizing in C9orf72, ATXN1 and ATXN2 was performed by fluorescent polymerase chain reaction (PCR) and capillary electrophoresis, while repeat-primed PCR was used to confirm C9orf72 expansions. APOE genotyping was conducted using real-time PCR assays targeting SNPs rs429358 and rs7412. Results: In the ALS/FTD cohort, 31.82% of the patients had heterozygous C9orf72 repeat expansion. The most common APOE genotype among patients was ε3/ε3 (72.73%). Intermediate-length ATXN1 alleles (32–44 repeats) were detected in 13.64% of patients and ATXN2 intermediate-length alleles (27–33 repeats) were found in 9% of patients. No significant differences were observed between ALS/FTD patients and controls in APOE ε4 frequency or intermediate ATXN1/ATXN2 repeats. Conclusions: Larger, population-specific studies and meta-analyses are needed to better understand the role of genetic modifiers in ALS/FTD pathogenesis and their influence on clinical heterogeneity. By integrating genetic and clinical data, this study represents a step toward the development of precision medicine strategies for ALS/FTD.

Background/Objectives: Glomerulonephritis (GNs) is a heterogeneous group of inflammatory kidney diseases. Novel genetic methods have revealed some disease-causing and susceptibility genes underlying primary and secondary GNs. We aimed to investigate the presence of the single nucleotide polymorphisms (SNPs) rs12917707, found in the UMOD gene, and rs17319721, found in the SHROOM3 gene, as well as different polymorphisms in immune system genes in a group of children with GN. Method: The study included 71 children with GN (40 with primary and 31 with secondary GN) and 119 healthy children (HC). SNPs of the UMOD (rs12917707), SHROOM3 (rs17319721), IL10 (rs1800871 and rs3024505), IL6 (rs1800795), IL12B (rs3212227), IL23R (rs11209026 and rs1800896), and TNF (rs361525 and rs1800629) genes were genotyped. Results: The median age of the patients was 8 years at the onset of GN and 14 years at sampling. Allele A for rs1800629 in the TNF gene was more common in patients with GN in comparison to HCs (p = 0.009), followed by the difference in genotype distributions (p = 0.021), where AA and GA genotypes were more prevalent in patients. We found a statistically significant difference in haplotype distributions between patients and HCs for TNF, with GN patients having the GGAG haplotype more frequently and HCs having GGGG (p < 0.05). No correlation between the investigated SNPs and patient clinical characteristics (disease onset, primary or secondary GN, severity of disease, occurrence of remission, and presence of hypertension) was observed. Conclusions: An association between the TNF gene and different types of GN was noticed in children with GN. This may help us to understand the pathogenesis of these disorders and develop new treatments to cover the unmet needs of children with GN.

Incontinentia pigmenti (IP) is a rare skin disease combined with anomalies of the teeth, eyes, and central nervous system (CNS). Mutations of the IKBKG gene are responsible for IP. Among the most frequent CNS abnormalities found in IP using magnetic resonance imaging (MRI) are corpus callosum (CC) abnormalities. The aim of the study was to determine the presence of CC abnormalities, their relationship with the IKBKG mutations, and the possible presence of mutations of other genes. A group of seven IP patients was examined. Analyses of the IKBKG gene and the X-chromosome inactivation pattern were performed, as well as MRI and whole exome sequencing (WES) with the focus on the genes relevant for neurodegeneration. WES analysis showed IKBKG mutation in all examined patients. A patient who had a mutation of a gene other than IKBKG was excluded from further study. Four of the seven patients had clinically diagnosed CNS anomalies; two out of four had MRI-diagnosed CC anomalies. The simultaneous presence of IKBKG mutation and CC abnormalities and the absence of other mutations indicate that IKBKG may be the cause of CC abnormalities and should be included in the list of genes responsible for CC abnormalities.

Hereditary spastic paraplegia (HSP) is among the most genetically diverse of all monogenic diseases. The aim was to analyze the genetic causes of HSP among adult Serbian patients. The study comprised 74 patients from 65 families clinically diagnosed with HSP during a nine-year prospective period. A panel of thirteen genes was analyzed: L1CAM (SPG1), PLP1 (SPG2), ATL1 (SPG3A), SPAST (SPG4), CYP7B1 (SPG5A), SPG7 (SPG7), KIF5A (SPG10), SPG11 (SPG11), ZYFVE26 (SPG15), REEP1 (SPG31), ATP13A2 (SPG78), DYNC1H1, and BICD2 using a next generation sequencing-based technique. A copy number variation (CNV) test for SPAST, SPG7, and SPG11 was also performed. Twenty-three patients from 19 families (29.2%) had conclusive genetic findings, including 75.0% of families with autosomal dominant and 25.0% with autosomal recessive inheritance, and 15.7% of sporadic cases. Twelve families had mutations in the SPAST gene, usually with a pure HSP phenotype. Three sporadic patients had conclusive findings in the SPG11 gene. Two unrelated patients carried a homozygous pathogenic mutation c.233T>A (p.L78*) in SPG7 that is a founder Roma mutation. One patient had a heterozygous de novo variant in the KIF5A gene, and one had a compound heterozygous mutation in the ZYFVE26 gene. The combined genetic yield of our gene panel and CNV analysis for HSP was around 30%. Our findings broaden the knowledge on the genetic epidemiology of HSP, with implications for molecular diagnostics in this region.

Rare diseases represent a diagnostic challenge due to their number, variety of clinical phenomena, and possibility of a simultaneous presence of two or more diseases. An illustration of this challenge is an occurrence of a late diagnosis of a proband initially diagnosed with West syndrome, later revealed to be caused by Incontinentia pigmenti (IP). Furthermore, 20 years later, it was discovered that the proband was also a carrier of a heterozygous GBA gene mutation. The methods used in diagnostics were as follows: IKBKG gene analysis, the X-chromosome inactivation assay, analyses of the genes relevant for neurodegeneration, WES analysis, analysis of biochemical parameters typical for Gaucher disease (GD), and autoantibodies including IFN-α2a and IFN-ω. To avoid overlooking IP and other possible rare disease diagnoses, carefully searching for dermatological signs in these conditions is recommended. It is important that the diagnostic criteria are based on quality and extensive data from multiple studies of each rare disease. Establishing precise diagnostic criteria for as many rare diseases as possible and establishing a publicly accessible database of rare diseases with a search possibility according to phenotypic abnormalities and genetic mutations would greatly facilitate and speed up the establishment of an accurate diagnosis.