Extensive clinical and genetic workup is worthwhile in patients with Leigh-like syndrome due to the TSFM variant c.547G>A


Homozygous frameshift variant in NTNG2 , encoding a synaptic cell adhesion molecule, in individuals with developmental delay, hypotonia, and autistic features

Abstract

Regulation of neuronal connectivity and synaptic communication are key to proper functioning of the brain. The Netrin-G subfamily and their cognate receptors are vertebrate-specific synaptic cell adhesion molecules with a role in synapse establishment and function, which seem to have co-evolved to contribute to higher brain functions. We identified a homozygous frameshift variant in NTNG2 (NM_032536.3: c.376dup), encoding Netrin-G2, in eight individuals from four families with global developmental delay, hypotonia, secondary microcephaly, and autistic features. Comparison of haplotypes established this as a founder variant. Previous studies showed that Ntng2-knockout mice have impaired visual, auditory, and motor coordination abilities required for demanding tasks, as well as possible spatial learning and memory deficits. Knockout of Ntng2 in a cellular model resulted in short neurites, and knockout of its trans-synaptic partner Ngl2/Lrrc4 in mice revealed autistic-like behavior and reduced NMDAR synaptic plasticity. The Ngl2/Lrrc4-knockout mouse phenotype was rescued by NMDAR activation, suggesting a mechanistic link to autism spectrum disorder. We thus propose NTNG2 as a candidate disease gene and provide further support for the involvement of Netrin-G2 in neuropsychiatric phenotypes.

Frequency of the LRRK2 G2019S mutation in South African patients with Parkinson’s disease

Abstract

G2019S in LRRK2 is the most common mutation associated with Parkinson’s disease (PD). Highest frequencies are in North African Arabic (30–41%) and Ashkenazi Jewish (6–30%) populations, mostly due to founder effects. Here, we investigated the frequency of G2019S in 647 unrelated South African PD patients from different ancestral origins. It was found in only 1.2% (8/647) of patients. Notably, none of the 91 individuals of African ancestry had G2019S. It was present in 1.9% (3/154) and 1% (5/493) of early- and late-onset cases, respectively. The frequency of G2019S exhibits ethnic-specific differences and warrants further study in sub-Saharan African populations.

VPS53 gene is associated with a new phenotype of complicated hereditary spastic paraparesis

Abstract

Hereditary spastic paraparesis (HSP) is a progressive neurodegenerative disorder, characterized by progressive lower limb weakness and spasticity. Multiple genes are associated with both the pure and complicated HSP types. Our study is aimed at seeking for novel genetic basis of HSP in a family with two affected siblings. Genetic analysis using whole exome sequencing was conducted in a family quartet with two female siblings, who presented with complicated HSP featuring slowly progressive paraparesis, mild-moderate intellectual disability, normal head circumference (HC), and normal magnetic resonance imaging (MRI). A homozygous pathogenic variant was identified in both siblings in the VPS53 gene (c.2084A>G: c.2084A>G, p.Gln695Arg). This gene acts as a component of the Golgi-associated retrograde protein (GARP) complex that is involved, among others, in intracellular cholesterol transport and sphingolipid homeostasis in lysosomes and was previously associated with progressive cerebello-cerebral atrophy (PCCA) type 2. This is the first description of the VPS53 gene as a cause of autosomal recessive complicated HSP. Lysosomal dysfunction as a result of impaired cholesterol trafficking can explain the neurodegenerative processes responsible for the HSP. Our finding expands the phenotype of VPS53-related disease and warrants the addition of VPS53 analysis to the genetic investigation in patients with autosomal recessive HSP. The exact role of GARP complex in neurodegenerative processes should be further elucidated.

Identification and characterization of novel and rare susceptible variants in Indian amyotrophic lateral sclerosis patients

Abstract

Rare missense variants play a crucial role in amyotrophic lateral sclerosis (ALS) pathophysiology. We report rare/novel missense variants from 154 Indian ALS patients, identified through targeted sequencing of 25 ALS-associated genes. As pathogenic variants could explain only a small percentage of ALS pathophysiology in our cohort, we investigated the frequency of tolerated and benign novel/rare variants, which could be potentially ALS susceptible. These variants were identified in 5.36% (8/149) of sporadic ALS (sALS) cases; with one novel variant each in ERBB4, SETX, DCTN1, and MATR3; four rare variants, one each in PON2 and ANG and two different rare variants in SETX. Identified variants were either absent or present at extremely rare frequencies (MAF < 0.01) in large population databases and were absent in 50 healthy controls sequenced through Sanger method. Furthermore, an oligogenic basis of ALS was observed in three sALS, with co-occurrence of intermediate-length repeat expansions in ATXN2 and a rare/novel variant in DCTN1 and SETX genes. Additionally, molecular dynamics and biochemical functional analysis of an angiogenin variant (R21G) identified from our cohort demonstrated loss of ribonucleolytic and nuclear translocation activities. Our findings suggest that rare variants could be potentially pathogenic and functional studies are warranted to decisively establish the pathogenic mechanisms associated with them.

Nervous NDRGs: the N-myc downstream–regulated gene family in the central and peripheral nervous system

Abstract

The N-Myc downstream-regulated gene (NDRG) family consists of four members (NDRG1, NDRG2, NDRG3, NDRG4) that are differentially expressed in various organs and function in important processes, like cell proliferation and differentiation. In the last couple of decades, interest in this family has risen due to its connection with several disorders of the nervous system including Charcot-Marie-Tooth disease and dementia, as well as nervous system cancers. By combining a literature review with in silico data analysis of publicly available datasets, such as the Mouse Brain Atlas, BrainSpan, the Genotype-Tissue Expression (GTEx) project, and Gene Expression Omnibus (GEO) datasets, this review summarizes the expression and functions of the NDRG family in the healthy and diseased nervous system. We here show that the NDRGs have a differential, relatively cell type–specific, expression pattern in the nervous system. Even though NDRGs share functionalities, like a role in vesicle trafficking, stress response, and neurite outgrowth, other functionalities seem to be unique to a specific member, e.g., the role of NDRG1 in myelination. Furthermore, mutations, phosphorylation, or changes in expression of NDRGs are related to nervous system diseases, including peripheral neuropathy and different forms of dementia. Moreover, NDRG1, NDRG2, and NDRG4 are all involved in cancers of the nervous system, such as glioma, neuroblastoma, or meningioma. All in all, our review elucidates that although the NDRGs belong to the same gene family and share some functional features, they should be considered unique in their expression patterns and functional importance for nervous system development and neuronal diseases.

Spasmodic dysphonia as a presenting symptom of spinocerebellar ataxia type 12

Abstract

Autosomal dominant spinocerebellar ataxia (SCA) type 12 is a rare SCA characterized by a heterogeneous phenotype. Action tremor of the upper limbs is the most common presenting sign and cerebellar signs can appear subsequently. In many cases, minor signs, like dystonia, can be predominant even at onset. Laryngeal dystonia (spasmodic dysphonia) has been observed only in one case of SCA12 and never reported at disease onset. We present a 61-year-old female who developed spasmodic dysphonia followed by dystonic tremor and subsequent ataxia diagnosed with SCA12. Thus, spasmodic dysphonia can be a presenting symptom of SCA12.

Novel homozygous TSFM pathogenic variant associated with encephalocardiomyopathy with sensorineural hearing loss and peculiar neuroradiologic findings

Abstract

TSFM is a nuclear gene encoding the elongation factor Ts (EFTs), an essential component of mitochondrial translational machinery. Impaired mitochondrial translation is responsible for neurodegenerative disorders characterized by multiple respiratory chain complex defects, multisystemic involvement, and neuroradiological features of Leigh-like syndrome. With the use of a next-generation sequencing (NGS)–based multigene panel for mitochondrial disorders, we identified the novel TSFM homozygous variant c.547G>A (p.Gly183Ser) in a 5-year-old boy with infantile early onset encephalocardiomyopathy, sensorineural hearing loss, and peculiar partially reversible neuroimaging features. Our findings expand the phenotypic spectrum of TSFM-related encephalopathy, offering new insights into the natural history of brain involvement and suggesting that TSFM should be investigated in pediatric mitochondrial disorders with distinctive neurologic and cardiac involvement.

A pathogenic CtBP1 missense mutation causes altered cofactor binding and transcriptional activity

Abstract

We previously reported a pathogenic de novo p.R342W mutation in the transcriptional corepressor CTBP1 in four independent patients with neurodevelopmental disabilities [1]. Here, we report the clinical phenotypes of seven additional individuals with the same recurrent de novo CTBP1 mutation. Within this cohort, we identified consistent CtBP1-related phenotypes of intellectual disability, ataxia, hypotonia, and tooth enamel defects present in most patients. The R342W mutation in CtBP1 is located within a region implicated in a high affinity-binding cleft for CtBP-interacting proteins. Unbiased proteomic analysis demonstrated reduced interaction of several chromatin-modifying factors with the CtBP1 W342 mutant. Genome-wide transcriptome analysis in human glioblastoma cell lines expressing -CtBP1 R342 (wt) or W342 mutation revealed changes in the expression profiles of genes controlling multiple cellular processes. Patient-derived dermal fibroblasts were found to be more sensitive to apoptosis during acute glucose deprivation compared to controls. Glucose deprivation strongly activated the BH3-only pro-apoptotic gene NOXA, suggesting a link between enhanced cell death and NOXA expression in patient fibroblasts. Our results suggest that context-dependent relief of transcriptional repression of the CtBP1 mutant W342 allele may contribute to deregulation of apoptosis in target tissues of patients leading to neurodevelopmental phenotypes.