Hereditary spastic paraparesis type 18 (SPG18): new ERLIN2 variants in a series of Italian patients, shedding light upon genetic and phenotypic variability.

INTRODUCTION: Hereditary spastic paraparesis (HSP) is a group of central nervous system diseases primarily affecting the spinal upper motor neurons, with different inheritance patterns and phenotypes. SPG18 is a rare, early-onset, complicated HSP, first reported as linked to biallelic ERLIN2 mutations. Recent cases of late-onset, pure HSP with monoallelic ERLIN2 variants prompt inquiries into the zygosity of such genetic conditions. The observed relationship between phenotype and mode of inheritance suggests a potential dominant negative effect of mutated ERLIN2 protein, potentially resulting in a milder phenotype. This speculation suggests that a wider range of HSP genes could be linked to various inheritance patterns. PURPOSE AND BACKGROUND: With documented cases of HSP loci exhibiting both dominant and recessive patterns, this study emphasizes that the concept of zygosity is no longer a limiting factor in the establishment of molecular diagnoses for HSP. Recent cases have demonstrated phenoconversion in SPG18, from HSP to an amyotrophic lateral sclerosis (ALS)-like syndrome. METHODS AND RESULTS: This report highlights two cases out of five exhibiting HSP-ALS phenoconversion, discussing an observed prevalence in autosomal dominant SPG18. Additionally, the study emphasizes the relatively high incidence of the c.502G>A variant in monoallelic SPG18 cases. This mutation appears to be particularly common in cases of HSPALS phenoconversion, indicating its potential role as a hotspot for a distinctive SPG18 phenotype with an ALS-like syndrome. CONCLUSIONS: Clinicians need to be aware that patients with HSP may show ALS signs and symptoms. On the other hand, HSP panels must be included in genetic testing methods for instances of familial ALS.

A Variant in TBCD Associated with Motoneuronopathy and Corpus Callosum Hypoplasia: A Case Report.

Mutations in the tubulin-specific chaperon D (TBCD) gene, involved in the assembly and disassembly of the α/ß-tubulin heterodimers, have been reported in early-onset progressive neurodevelopment regression, with epilepsy and mental retardation. We describe a rare homozygous variant in TBCD, namely c.881G>A/p.Arg294Gln, in a young woman with a phenotype dominated by distal motorneuronopathy and mild mental retardation, with neuroimaging evidence of corpus callosum hypoplasia. The peculiar phenotype is discussed in light of the molecular interpretation, enriching the literature data on tubulinopathies generated from TBCD mutations.

A new genetic cause of spastic ataxia: the p.Glu415Lys variant in TUBA4A.

Tubulinopathies encompass neurodevelopmental disorders caused by mutations in genes encoding for different isotypes of α- and ß-tubulins, the structural components of microtubules. Less frequently, mutations in tubulins may underlie neurodegenerative disorders. In the present study, we report two families, one with 11 affected individuals and the other with a single patient, carrying a novel, likely pathogenic, variant (p. Glu415Lys) in the TUBA4A gene (NM_006000). The phenotype, not previously described, is that of spastic ataxia. Our findings widen the phenotypic and genetic manifestations of TUBA4A variants and add a new type of spastic ataxia to be taken into consideration in the differential diagnosis.

Power of NGS-based tests in HSP diagnosis: analysis of massively parallel sequencing in clinical practice.

Hereditary spastic paraplegia (HSP) refers to a group of heterogeneous neurological disorders mainly characterized by corticospinal degeneration (pure forms), but sometimes associated with additional neurological and extrapyramidal features (complex HSP). The advent of next-generation sequencing (NGS) has led to huge improvements in knowledge of HSP genetics and made it possible to clarify the genetic etiology of hundreds of "cold cases," accelerating the process of reaching a molecular diagnosis. The different NGS-based strategies currently employed as first-tier approaches most commonly involve the use of targeted resequencing panels and exome sequencing, whereas genome sequencing remains a second-tier approach because of its high costs. The question of which approach is the best is still widely debated, and many factors affect the choice. Here, we aim to analyze the diagnostic power of different NGS techniques applied in HSP, by reviewing 38 selected studies in which different strategies were applied in different-sized cohorts of patients with genetically uncharacterized HSP.

CUL4B-associated epilepsy: Report of a novel truncating variant promoting drug-resistant seizures and systematic review of the literature.

BACKGROUND: Cabezas syndrome is a rare X-linked disease caused by mutations in CUL4B and characterized by developmental delay/intellectual disability, somatic dysmorphisms, behavioural disorder, ataxia/tremors. Although seizures have been formerly reported, their clinical semiology, EEG features and long-term outcome are largely unknown. PURPOSE: This study aims to expand knowledge on epilepsy associated with Cabezas syndrome and to understand whether different types of variants in the CUL4B gene or brain MRI abnormalities may influence seizure onset and epilepsy course. METHODS: With this in mind, we characterised the epileptic phenotype of a 17-year-old adolescent harbouring a CUL4B novel variant and performed a systematic literature review of CUL4B-associated seizures, analysing mutation types and neuroimaging features as epilepsy predictors. RESULTS: Our case observation indicates that CUL4B-associated epilepsy may also be drug-resistant and persist beyond infancy. Literature analysis shows that 43% of CUL4B patients develop seizures, with no statistically significant differences in epilepsy development according to mutation type and neuroimaging features. CONCLUSION: Our study extends knowledge of CUL4B-associated epilepsy, offering new insights into disease progression.

Clinical-Genetic Features Influencing Disability in Spastic Paraplegia Type 4: A Cross-sectional Study by the Italian DAISY Network.

Background and Objectives: Hereditary spastic paraplegias (HSPs) are a group of inherited rare neurologic disorders characterized by length-dependent degeneration of the corticospinal tracts and dorsal columns, whose prominent clinical feature is represented by spastic gait. Spastic paraplegia type 4 (SPG4, SPAST-HSP) is the most common form. We present both clinical and molecular findings of a large cohort of patients, with the aim of (1) defining the clinical spectrum of SPAST-HSP in Italy; (2) describing their molecular features; and (3) assessing genotype-phenotype correlations to identify features associated with worse disability. Methods: A cross-sectional retrospective study with molecular and clinical data collected in an anonymized database was performed. Results: A total of 723 Italian patients with SPAST-HSP (58% men) from 316 families, with a median age at onset of 35 years, were included. Penetrance was 97.8%, with men showing higher Spastic Paraplegia Rating Scale (SPRS) scores (19.67 ± 12.58 vs 16.15 ± 12.61, p = 0.009). In 26.6% of patients with SPAST-HSP, we observed a complicated phenotype, mainly including intellectual disability (8%), polyneuropathy (6.7%), and cognitive decline (6.5%). Late-onset cases seemed to progress more rapidly, and patients with a longer disease course displayed a more severe neurologic disability, with higher SPATAX (3.61 ± 1.46 vs 2.71 ± 1.20, p < 0.001) and SPRS scores (22.63 ± 11.81 vs 12.40 ± 8.83, p < 0.001). Overall, 186 different variants in the SPAST gene were recorded, of which 48 were novel. Patients with SPAST-HSP harboring missense variants displayed intellectual disability (14.5% vs 4.4%, p < 0.001) more frequently, whereas patients with truncating variants presented more commonly cognitive decline (9.7% vs 2.6%, p = 0.001), cerebral atrophy (11.2% vs 3.4%, p = 0.003), lower limb spasticity (61.5% vs 44.5%), urinary symptoms (50.0% vs 31.3%, p < 0.001), and sensorimotor polyneuropathy (11.1% vs 1.1%, p < 0.001). Increasing disease duration (DD) and abnormal motor evoked potentials (MEPs) were also associated with increased likelihood of worse disability (SPATAX score>3). Discussion: The SPAST-HSP phenotypic spectrum in Italian patients confirms a predominantly pure form of HSP with mild-to-moderate disability in 75% of cases, and slight prevalence of men, who appeared more severely affected. Early-onset cases with intellectual disability were more frequent among patients carrying missense SPAST variants, whereas patients with truncating variants showed a more complicated disease. Both longer DD and altered MEPs are associated with worse disability.

Correlation among maternal risk factors, gene methylation and disease severity in females with autism spectrum disorder.

Aim: To detect early-life environmental factors leading to DNA methylation changes of autism spectrum disorder (ASD)-related genes in young ASD females and reveal epigenetic biomarkers of disease severity. Materials & methods: We investigated blood methylation levels of MECP2, OXTR, BDNF, RELN, BCL2, EN2 and HTR1A genes in 42 ASD females. Results: Maternal gestational weight gain correlated with BDNF methylation levels (Bonferroni-corrected p = 0.034), and lack of folic acid supplementation at periconception resulted in higher disease severity in the ASD children (Bonferroni-corrected p = 0.048). RELN methylation levels were inversely correlated with disease severity (Bonferroni corrected p = 0.042). Conclusion: The present study revealed gene-environment interactions and potential epigenetic biomarkers of disease severity in ASD females.

Early-life maternal factors can leave marks on the DNA of the developing fetus, including changes in DNA methylation that regulate gene expression levels. These marks can pose an increased risk for several diseases, such as autism spectrum disorder (ASD) and other developmental disorders. In the present study, we searched for links between early-life maternal factors and the methylation levels of ASD-related genes in blood DNA samples of young ASD diagnosed females. We found that high maternal gestational weight gain resulted in increased methylation levels of the BDNF gene, one of the most important genes for brain development. Moreover, lack of maternal folic acid supplementation and low RELN methylation levels resulted in higher disease severity in ASD females.

NGS in Hereditary Ataxia: When Rare Becomes Frequent.

The term hereditary ataxia (HA) refers to a heterogeneous group of neurological disorders with multiple genetic etiologies and a wide spectrum of ataxia-dominated phenotypes. Massive gene analysis in next-generation sequencing has entered the HA scenario, broadening our genetic and clinical knowledge of these conditions. In this study, we employed a targeted resequencing panel (TRP) in a large and highly heterogeneous cohort of 377 patients with a clinical diagnosis of HA, but no molecular diagnosis on routine genetic tests. We obtained a positive result (genetic diagnosis) in 33.2% of the patients, a rate significantly higher than those reported in similar studies employing TRP (average 19.4%), and in line with those performed using exome sequencing (ES, average 34.6%). Moreover, 15.6% of the patients had an uncertain molecular diagnosis. STUB1, PRKCG, and SPG7 were the most common causative genes. A comparison with published literature data showed that our panel would have identified 97% of the positive cases reported in previous TRP-based studies and 92% of those diagnosed by ES. Proper use of multigene panels, when combined with detailed phenotypic data, seems to be even more efficient than ES in clinical practice.

Neuroimaging patterns in paediatric onset hereditary spastic paraplegias.

Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by progressive spasticity and weakness of the lower limbs with a notable phenotypic variation and an autosomal recessive (AR), autosomal dominant (AD), and X-linked inheritance pattern. The recent clinical use of next generation sequencing methods has facilitated the diagnostic approach to HSPs, but the diagnosis remains quite challenging considering its wide clinical and genetic heterogeneity. In this scenario, magnetic resonance imaging (MRI) emerges as a valuable tool in helping to exclude mimicking disorders and to guide genetic testing. The aim of this study is to investigate the presence of possible patterns of morphostructural MRI findings that may provide relevant clues for a specific genetic HSP subtype. In our cohort, for example, white matter abnormalities were the most common finding followed by the thinning of the corpus callosum, which, interestingly, presented different thinning characteristics depending on the HSP subtype.

Multimodal evaluation of an Italian family with a hereditary spastic paraplegia and POLR3A mutations.

We describe an Italian family with adult-onset pure hereditary spastic paraplegia due to biallelic variants in POLR3A gene [c.1909 + 22G > A and c.3839dupT (p.M1280fs*20]. MRI showed a mild hyperintensity of superior cerebellar peduncles and cervical spinal cord atrophy. The neurophysiological metrics about intracortical excitability showed higher values of motor thresholds and a significant reduction of short interval intracortical inhibition (SICI) in the patient with a more severe phenotype. Our multimodal evaluation further expands the wide phenotypic spectrum associated with mutations in the POLR3A gene. An extensive genotype-phenotype correlation study is necessary to explain the role of the many new mutations on the function of protein.

Docosahexaenoic acid in ARSACS: observations in two patients.

BACKGROUND: Spastic ataxia of Charlevoix-Saguenay is a neurodegenerative condition due to mutations in the SACS gene and without a cure. Attempts to treatments are scarce and limited to symptomatic drugs. CASE PRESENTATION: Two siblings harboring biallelic variants in SACS underwent oral supplementation (600 mg/die) with docosahexaenoic acid (DHA), a well-tolerated dietary supplement currently used in SCA38 patients. We assessed over a 20 month-period clinical progression using disease-specific rating scales. CONCLUSIONS: DHA was safe over a long period and well-tolerated by the two patients; both showed a stabilization of clinical symptoms, rather than the expected deterioration, warranting additional investigations in patients with mutations in SACS.

Spinocerebellar ataxia type 48: last but not least.

INTRODUCTION: Biallelic mutations in STUB1, which encodes the E3 ubiquitin ligase CHIP, were originally described in association with SCAR16, a rare autosomal recessive spinocerebellar ataxia, so far reported in 16 kindreds. In the last 2 years, a new form of spinocerebellar ataxia (SCA48), associated with heterozygous mutations in the same gene, has been described in 12 kindreds with autosomal dominant inheritance. METHODS: We reviewed molecular and clinical findings of both SCAR16 and SCA48 described patients. RESULTS AND CONCLUSION: SCAR16 is characterized by early onset spastic ataxia and a wide disease spectrum, including cognitive dysfunction, hyperkinetic disorders, epilepsy, peripheral neuropathy, and hypogonadism. SCA48 is an adult-onset syndrome characterized by ataxia and cognitive-psychiatric features, variably associated with chorea, parkinsonism, dystonia, and urinary symptoms. SCA48, the last dominant ataxia to be described, could emerge as the most frequent among the SCAs due to conventional mutations. The overlap of several clinical signs between SCAR16 and SCA48 indicates the presence of a continuous clinical spectrum among recessively and dominantly inherited mutations of STUB1. Different kinds of mutations, scattered over the three gene domains, have been found in both disorders. Their pathogenesis and the relationship between SCA48 and SCAR16 remain to be clarified.

Broad phenotypic spectrum and genotype-phenotype correlations in GMPPB-related dystroglycanopathies: an Italian cross-sectional study.

BACKGROUND: Dystroglycanopathy (α-DG) is a relatively common, clinically and genetically heterogeneous category of congenital forms of muscular dystrophy (CMD) and limb-girdle muscular dystrophy (LGMD) associated with hypoglycosylated α-dystroglycan. To date, mutations in at least 19 genes have been associated with α-DG. One of them, GMPPB, encoding the guanosine-diphosphate-mannose (GDP-mannose) pyrophosphorylase B protein, has recently been associated with a wide clinical spectrum ranging from severe Walker-Warburg syndrome to pseudo-metabolic myopathy and even congenital myasthenic syndromes. We re-sequenced the full set of known disease genes in 73 Italian patients with evidence of either reduced or nearly absent α-dystroglycan to assess genotype-phenotype correlations in this cohort. We used innovative bioinformatic tools to calculate the effects of all described GMPPB mutations on protein function and attempted to correlate them with phenotypic expressions. RESULTS: We identified 13 additional cases from 12 families and defined seven novel mutations. Patients displayed variable phenotypes including less typical pictures, ranging from asymptomatic hyperCKemia, to arthrogryposis and congenital clubfoot at birth, and also showed neurodevelopmental comorbidities, such as seizures and ataxic gait, as well as autism-spectrum disorder, which is seldom described in clinical reports of dystroglycanopathies. We also demonstrated that few mutations recur in the Italian GMPPB-mutated population and that alterations of protein stability are the main effects of GMPPB missense variants. CONCLUSION: This work adds to the data on genotype-phenotype correlations in α-DG and offers new bionformatic tools to provide the conceptual framework needed to understand the complexity of these disorders.

Congenital myopathies: clinical phenotypes and new diagnostic tools.

Congenital myopathies are a group of genetic muscle disorders characterized clinically by hypotonia and weakness, usually from birth, and a static or slowly progressive clinical course. Historically, congenital myopathies have been classified on the basis of major morphological features seen on muscle biopsy. However, different genes have now been identified as associated with the various phenotypic and histological expressions of these disorders, and in recent years, because of their unexpectedly wide genetic and clinical heterogeneity, next-generation sequencing has increasingly been used for their diagnosis. We reviewed clinical and genetic forms of congenital myopathy and defined possible strategies to improve cost-effectiveness in histological and imaging diagnosis.

Myoimaging in the NGS era: the discovery of a novel mutation in MYH7 in a family with distal myopathy and core-like features--a case report.

BACKGROUND: Myosin heavy chain 7 related myopathies are rare disorders characterized by a wide phenotypic spectrum and heterogeneous pathological features. In the present study, we performed clinical, morphological, genetic and imaging investigations in three relatives affected by autosomal dominant distal myopathy. Whilst earlier traditional Sanger investigations had pointed to the wrong gene as disease causative, next-generation sequencing allowed us to obtain the definitive molecular genetic diagnosis in the family. CASE PRESENTATION: The proposita, being found to harbor a novel heterozygous mutation in the RYR1 gene (p.Glu294Lys), was initially diagnosed with core myopathy. Subsequently, consideration of muscle magnetic resonance imaging (MRI) features and extension of family study led this diagnosis to be questioned. Use of next-generation sequencing analysis identified a novel mutation in the MYH7gene (p.Ser1435Pro) that segregated in the affected family members. CONCLUSIONS: This study identified a novel mutation in MYH7 in a family where the conclusive molecular diagnosis was reached through a complicated path. This case report might raise awareness, among clinicians, of the need to interpret NGS data in combination with muscle MRI patterns so as to facilitate the pinpointing of the main molecular etiology in inherited muscle disorders.

A diagnostic dilemma in a family with cystinuria type B resolved by muscle magnetic resonance.

BACKGROUND: Congenital myopathies are inherited primary disorders of the muscle caused by mutations affecting structural, contractile, or regulatory proteins. In the more than 20 genes associated to these conditions, ryanodine receptor type 1 gene (RYR1) is responsible for the most common forms and is associated with a wide range of clinical phenotypes and pathological findings. Magnetic resonance imaging of muscle has been used increasingly to direct genetic testing in myopathies. PATIENT DESCRIPTION: We describe a consanguineous family affected by cystinuria type B, a metabolic condition linked to chromosome 19q13.2, and a different muscle phenotype that, although related to a congenital myopathy, does not have the striking histological features helping in direct genetic tests. RESULTS: The assessment of the selective involvement on muscle magnetic resonance imaging allowed the suspicion of RYR1 as the most likely gene responsible for this myopathy. The diagnosis was subsequently confirmed by the finding of a recessive RYR1 mutation. CONCLUSIONS: The occurrence of congenital myopathy together with cystinuria type B is reported for the first time. The use of muscle magnetic resonance imaging and the homozygosity by descent in SLC7A9, a gene flanking RYR1, allowed us to discover a new mutation in the RYR1 gene.

Elevated serum creatine kinase and small cerebellum prompt diagnosis of congenital muscular dystrophy due to FKRP mutations.

Fukutin-related protein (FKRP) is a putative glycosyltransferase that mediate O-linked glycosylation of the α-dystroglycan. Mutations in the FKRP gene cause a spectrum of diseases ranging from a limb girdle muscular dystrophy 2I (LGMD2I), to severe Walker-Warburg or muscle-eye-brain forms and a congenital muscular dystrophy (with or without mental retardation) termed MDC1C. This article reports on a Moroccan infant who presented at birth with moderate floppiness, high serum creatine kinase (CK) levels, and brain ultrasonograph suggestive of widening of the posterior fossa. Muscle biopsy displayed moderate dystrophic pattern with complete absence of α-distroglycan and genetic studies identified a homozygous missense variant in FKRP. Mutations in FKRP should be looked for in forms of neonatal-onset hyperCKaemia with floppiness and small cerebellum.

EXOSC3 mutations in isolated cerebellar hypoplasia and spinal anterior horn involvement.

Pontocerebellar hypoplasia (PCH) type 1 is characterized by the co-occurrence of spinal anterior horn involvement and hypoplasia of the cerebellum and pons. EXOSC3 has been recently defined as a major cause of PCH type 1. Three different phenotypes showing variable severity have been reported. We identified a homozygous mutation [c.395A > C/p.D132A] in EXOSC3 in four patients with muscle hypotonia, developmental delay, spinal anterior horn involvement, and prolonged survival, consistent with the "mild PCH1 phenotype". Interestingly, isolated cerebellar hypoplasia limited to the hemispheres or involving both hemispheres and vermis was the main neuroradiologic finding, whereas the pontine volume was in the normal range for age. These findings strongly suggest that analysis of the EXOSC3 gene should be recommended also in patients with spinal anterior horn involvement and isolated cerebellar hypoplasia.