AP2A2 mutation and defective endocytosis in a Malian family with hereditary spastic paraplegia.

Hereditary spastic paraplegia (HSP) comprises a large group of neurogenetic disorders characterized by progressive lower extremity spasticity. Neurological evaluation and genetic testing were completed in a Malian family with early-onset HSP. Three children with unaffected consanguineous parents presented with symptoms consistent with childhood-onset complicated HSP. Neurological evaluation found lower limb weakness, spasticity, dysarthria, seizures, and intellectual disability. Brain MRI showed corpus callosum thinning with cortical and spinal cord atrophy, and an EEG detected slow background in the index patient. Whole exome sequencing identified a homozygous missense variant in the adaptor protein (AP) complex 2 alpha-2 subunit (AP2A2) gene. Western blot analysis showed reduced levels of AP2A2 in patient-iPSC derived neuronal cells. Endocytosis of transferrin receptor (TfR) was decreased in patient-derived neurons. In addition, we observed increased axon initial segment length in patient-derived neurons. Xenopus tropicalis tadpoles with ap2a2 knockout showed cerebral edema and progressive seizures. Immunoprecipitation of the mutant human AP-2-appendage alpha-C construct showed defective binding to accessory proteins. We report AP2A2 as a novel genetic entity associated with HSP and provide functional data in patient-derived neuron cells and a frog model. These findings expand our understanding of the mechanism of HSP and improve the genetic diagnosis of this condition.

Pentanucleotide Repeat Insertions in RAI1 Cause Benign Adult Familial Myoclonic Epilepsy Type 8.

BACKGROUND: Benign adult familial myoclonic epilepsy (BAFME) is an autosomal dominant disorder characterized by cortical tremors and seizures. Six types of BAFME, all caused by pentanucleotide repeat expansions in different genes, have been reported. However, several other BAFME cases remain with no molecular diagnosis. OBJECTIVES: We aim to characterize clinical features and identify the mutation causing BAFME in a large Malian family with 10 affected members. METHODS: Long-read whole genome sequencing, repeat-primed polymerase chain reaction and RNA studies were performed. RESULTS: We identified TTTTA repeat expansions and TTTCA repeat insertions in intron 4 of the RAI1 gene that co-segregated with disease status in this family. TTTCA repeats were absent in 200 Malian controls. In the affected individuals, we found a read with only nine TTTCA repeat units and somatic instability. The RAI1 repeat expansions cause the only BAFME type in which the disease-causing repeats are in a gene associated with a monogenic disorder in the haploinsufficiency state (ie, Smith-Magenis syndrome [SMS]). Nevertheless, none of the Malian patients exhibited symptoms related to SMS. Moreover, leukocyte RNA levels of RAI1 in six Malian BAFME patients were no different from controls. CONCLUSIONS: These findings establish a new type of BAFME, BAFME8, in an African family and suggest that haploinsufficiency is unlikely to be the main pathomechanism of BAFME. © 2023 International Parkinson and Movement Disorder Society. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Novel variant in CADM3 causes Charcot-Marie-Tooth disease.

CADM3 has been recently reported causing a rare axonal Charcot-Marie-Tooth disease in three independent Caucasian families carrying a recurrent change. We describe the first alternative causative mutation in CADM3 in a family from black African and also observed de novo in a patient of Caucasian ancestry. The disease inheritance was consistent with autosomal dominant and sporadic patterns, respectively. Eight patients and their relatives were enroled from both families. The mean age at diagnosis was 33.9 years, and walking difficulty was commonly the first symptom. Neurological examination showed distal muscle weakness and atrophy, sensory loss and foot and hand deformities. A high clinical variability was noted, but as seen in CADM3-associated neuropathy, symptoms were more pronounced in the arms in some patients. Nerve conduction studies showed no response in most of the examined nerves, and an axonal type of neuropathy, where recorded. Whole exome sequencing revealed a novel missense variant (c.1102G>T; Gly368Cys) in CADM3, segregating with the disease. Functional analyses showed a significant decrease in CADM3-Gly368Cys protein levels in the membrane and major structural changes in its predicted secondary structure. Therefore, we extend the genotype spectrum of CADM3, underlining the need for genetic studies in underrepresented populations like in Africa.

Hereditary spastic paraplegia in Mali: epidemiological and clinical features.

BACKGROUND AND PURPOSE: Hereditary spastic paraplegia (HSP) is a group of neurodegenerative diseases divided into pure and complex forms, with spasticity in lower limbs only, or associated with other neurologic and non-neurologic manifestations, respectively. Although widely reported in other populations, very little data exist in sub-Saharan Africa. METHODS: Patients with neurodegenerative features were evaluated over a 19-month period at the Department of Neurology, Teaching Hospital of Point "G", Bamako, Mali. The diagnosis of HSP was considered based on family history and the absence of other known non-genetic causes. Genetic analysis including candidate gene and whole exome sequencing was performed and variant pathogenicity was tested using prediction tools and ACMG guidelines. RESULTS: Of the 170 families with hereditary neurological disorders enrolled, 16 had features consistent with HSP, a frequency of 9%. The average age of onset was 14.7 years with 46% starting before age 6. The male/female ratio was 2.6:1. Complex forms were seen in 75% of cases, and pure forms in 25%. Pyramidal findings were present in all patients. Associated features included mental retardation, peripheral neuropathy, epilepsy, oculomotor impairment and urinary urgency. Most patients were treated with a muscle relaxant and physical therapy, and restorative surgery was done in one. Genetic testing identified novel variants in three families (19%). CONCLUSION: This study confirms the clinical variability of HSPs and adds African data to the current literature.

SAFETY AND TOLERABILITY OF STRENGTH TRAINING IN SPINAL AND BULBAR MUSCULAR ATROPHY: A CASE REPORT.

Objective: Spinal and bulbar muscular atrophy is characterized by slow-progressive muscle weakness, decreased functional performance and falls. Research into the use of exercise in spinal and bulbar muscular atrophy has shown equivocal to negative results, although authors suggest that patients with spinal and bulbar muscular atrophy may benefit from both increased exercise intensity and shorter bout duration. The aim of this case report is to explore the safety of a moderate intensity strength training programme coupled with dynamic balance and function-specific training in a patient with spinal and bulbar muscular atrophy. Case report: A 56-year-old man with spinal and bulbar muscular atrophy presented with multiple falls and declining performance in physical, vocational, and recreational activities. Examination revealed several musculoskeletal impairments that were sub-clinical to mild compared with an SBMA natural history cohort. Intervention and outcome: A 15-week moderate intensity exercise programme combining weight-lifting and functional exercises was performed under clinical supervision. Exercise volume, frequency and intensity were adjusted based on patient-reported outcomes and muscle damage blood markers. Performance-based and self-reported functional improvements occurred that exceeded the minimal clinically important difference. The intervention was well tolerated and the patient nearly doubled his baseline 10-repetition maximums for weight-lifting exercises. Conclusion: Exercise therapy combining weight-lifting and upright functional training led to meaningful performance improvements in this case of a patient with spinal and bulbar muscular atrophy and relatively low disease burden.

Altered SYNJ2BP-mediated mitochondrial-ER contacts in motor neuron disease.

Synaptojanin 2 binding protein (SYNJ2BP) is an outer mitochondrial membrane protein with a cytosolic PDZ domain that functions as a cellular signaling hub. Few studies have evaluated its role in disease. Here we use induced pluripotent stem cell (iPSC)-derived motor neurons and post-mortem tissue from patients with two hereditary motor neuron diseases, spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis type 4 (ALS4), and show that SYNJ2BP expression is increased in diseased motor neurons. Similarly, we show that SYNJ2BP expression increases in iPSC-derived motor neurons undergoing stress. Using proteomic analysis, we found that elevated SYNJ2BP alters the cellular distribution of mitochondria and increases mitochondrial-ER membrane contact sites. Furthermore, decreasing SYNJ2BP levels improves mitochondrial oxidative function in the diseased motor neurons. Together, our observations offer new insight into the molecular pathology of motor neuron disease and the role of SYNJ2BP in mitochondrial dysfunction.

Nonalcoholic Fatty Liver Disease in Patients with Inherited and Sporadic Motor Neuron Degeneration.

We describe evidence of fatty liver disease in patients with forms of motor neuron degeneration with both genetic and sporadic etiology compared to controls. A group of 13 patients with motor neuron disease underwent liver imaging and laboratory analysis. The cohort included five patients with hereditary spastic paraplegia, four with sporadic amyotrophic lateral sclerosis (ALS), three with familial ALS, and one with primary lateral sclerosis. A genetic mutation was reported in nine of the thirteen motor neuron disease (MND) patients. Fatty liver disease was detected in 10 of 13 (77%) MND patients via magnetic resonance spectroscopy, with an average dome intrahepatic triacylglycerol content of 17% (range 2-63%, reference ≤5.5%). Liver ultrasound demonstrated evidence of fatty liver disease in 6 of the 13 (46%) patients, and serum liver function testing revealed significantly elevated alanine aminotransferase levels in MND patients compared to age-matched controls. Fatty liver disease may represent a non-neuronal clinical component of various forms of MND.

GJB1 variants in Charcot-Marie-Tooth disease X-linked type 1 in Mali.

X-linked Charcot-Marie-Tooth type 1 (CMTX1) disease is one of the most common subtypes of inherited neuropathies and is caused by mutations in the GJB1 gene. To date, more than 400 mutations have been reported in GJB1 worldwide but none in sub-Saharan Africa (SSA). We aimed to clinically characterize patients with CMTX1 and identify the genetic defects. All patients were examined thoroughly, and Nerve Conduction Studies (NCS) were done. EEG and pure tone audiometry (PTA) were also done in select individuals having additional symptoms. DNA was extracted for CMT gene panel testing (50 genes + mtDNA and PMP22 duplication), and putative variants were screened in available relatives. The predominant starting symptom was tingling, and the chief complaint was gait difficulty. Neurological examination found a distal muscle weakness and atrophy, and sensory loss, skeletal deformities, decreased or absent reflexes and steppage gait. The inheritance pattern was consistent with dominant X-linked. NCS showed no response in most of the tested nerves in lower limbs, and normal or reduced amplitudes in upper limbs. A severe sensorineural hearing impairment and a focal epileptic seizure were observed in one patient each. A high intra and inter-familial clinical variability was observed. Genetic testing found three pathogenic missense variants in GJB1, one in each of the families (Val91Met, Arg15Trp, and Phe235Cys). This is the first report of genetically confirmed cases of CMTX1 in SSA, and confirms its clinical and genetic heterogeneity.

Clinical and Genetic Aspects of Huntington's Disease in the Malian Population.

BACKGROUND: Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by mutation in the HTT gene and characterized by involuntary movements as well as cognitive and behavioral impairment. Since its first description 150 years ago, studies have been reported worldwide. However, genetically confirmed cases have been scarce in Africa. OBJECTIVE: To describe the clinical and genetic aspects of HD in the Malian population. METHODS: Patients with HD phenotype and their relatives were enrolled after obtaining consent. Symptoms were assessed using the Total Motor Scale (TMS) of the United Huntington's Disease Rating Scale (UHDRS) and the Mini-Mental State Examination (MMSE). Brain imaging and blood tests were performed to exclude other causes. DNA was extracted for HTT sequencing. RESULTS: Eighteen patients (13 families) with a HD phenotype were evaluated. A familial history of the disease was found in 84.6% with 55.5% of maternal transmission. The average length of the HTT CAG repeat was 43.6±11.5 (39-56) CAGs. The mean age at onset was 43.1±9.7years. Choreic movements were the predominant symptoms (100% of the cases) with an average TMS of 49.4±30.8, followed by cognitive impairment (average MMSE score: 23.0±12.0) and psychiatric symptoms with 22.2% and 44.4%, respectively. CONCLUSION: This is one of the largest HD cohorts reported in Africa. Increasing access to genetic testing could uncover many other HD cases and disease-modifying genetic variants. Future haplotype and psychosocial studies may inform the origin of the Malian mutation and the impact of the disease on patients and their relatives.

Variants in ATP6V0A1 cause progressive myoclonus epilepsy and developmental and epileptic encephalopathy.

The vacuolar H+-ATPase is a large multi-subunit proton pump, composed of an integral membrane V0 domain, involved in proton translocation, and a peripheral V1 domain, catalysing ATP hydrolysis. This complex is widely distributed on the membrane of various subcellular organelles, such as endosomes and lysosomes, and plays a critical role in cellular processes ranging from autophagy to protein trafficking and endocytosis. Variants in ATP6V0A1, the brain-enriched isoform in the V0 domain, have been recently associated with developmental delay and epilepsy in four individuals. Here, we identified 17 individuals from 14 unrelated families with both with new and previously characterized variants in this gene, representing the largest cohort to date. Five affected subjects with biallelic variants in this gene presented with a phenotype of early-onset progressive myoclonus epilepsy with ataxia, while 12 individuals carried de novo missense variants and showed severe developmental and epileptic encephalopathy. The R740Q mutation, which alone accounts for almost 50% of the mutations identified among our cases, leads to failure of lysosomal hydrolysis by directly impairing acidification of the endolysosomal compartment, causing autophagic dysfunction and severe developmental defect in Caenorhabditis elegans. Altogether, our findings further expand the neurological phenotype associated with variants in this gene and provide a direct link with endolysosomal acidification in the pathophysiology of ATP6V0A1-related conditions.

Dynamic Balance in Spinal and Bulbar Muscular Atrophy: Relationship between Strength and Performance of Forward Lunge, Step Up and Over, and Step Quick Turn.

INTRODUCTION: Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disorder that leads to progressive weakness of bulbar and extremity muscles. Dynamic balance during functional tasks has not been reported in people with SBMA. OBJECTIVES: (1) To evaluate the ability to safely complete a forward lunge (FL), step quick turn (SQT), and step up and over (SUO), (2) to determine the presence and severity of dynamic balance impairments by comparing performance to normative data, and (3) to investigate the relationship between lower extremity strength and ability to complete each task. DESIGN: Cross-sectional analysis. Participants. Fifty-three people with SBMA were included in a cross-sectional analysis. Normative datasets provided by the NeuroCom manufacturer and isometric strength literature facilitated patient comparisons. Outcome Measures. Force plate-based dynamic balance measures included FL (distance, impact index, contact time, and force impulse), SQT (turn time and turn sway), and SUO (lift up index, movement time, and impact index). Maximal isometric contractions of knee extensors, ankle dorsiflexors, ankle plantar flexors, and hip extensors were measured with fixed frame dynamometry. RESULTS: The most difficult test, per completion rate, was SUO (52%), followed by FL (57%) and SQT (65%). t-tests revealed significant abnormalities in eight of nine balance variables (p < 0.05) accompanied by large Cohen's D effect sizes ≥ 0.8. Receiver operating characteristics analysis showed knee extensor (SUO 95% CI =0.78-1.00, SQT 95% CI =0.64-0.92) and ankle plantar flexor strength (SUO 95%CI = 0.75-0.99, SQT 95%CI = 0.64 - 0.92) significantly discriminated the ability to perform SUO and SQT tests with acceptable to excellent areas under the curve. CONCLUSIONS: Considerable dynamic balance abnormalities were observed. Lower extremity strength helps explain low test completion rates. Patients modified task movement patterns, enabling safe task performance. Study results can help direct patient care and future protocol design for people with SBMA.

Gene therapy with AR isoform 2 rescues spinal and bulbar muscular atrophy phenotype by modulating AR transcriptional activity.

Spinal and bulbar muscular atrophy (SBMA) is an X-linked, adult-onset neuromuscular condition caused by an abnormal polyglutamine (polyQ) tract expansion in androgen receptor (AR) protein. SBMA is a disease with high unmet clinical need. Recent studies have shown that mutant AR-altered transcriptional activity is key to disease pathogenesis. Restoring the transcriptional dysregulation without affecting other AR critical functions holds great promise for the treatment of SBMA and other AR-related conditions; however, how this targeted approach can be achieved and translated into a clinical application remains to be understood. Here, we characterized the role of AR isoform 2, a naturally occurring variant encoding a truncated AR lacking the polyQ-harboring domain, as a regulatory switch of AR genomic functions in androgen-responsive tissues. Delivery of this isoform using a recombinant adeno-associated virus vector type 9 resulted in amelioration of the disease phenotype in SBMA mice by restoring polyQ AR-dysregulated transcriptional activity.

Improving the efficacy of exome sequencing at a quaternary care referral centre: novel mutations, clinical presentations and diagnostic challenges in rare neurogenetic diseases.

BACKGROUND: We used a multimodal approach including detailed phenotyping, whole exome sequencing (WES) and candidate gene filters to diagnose rare neurological diseases in individuals referred by tertiary neurology centres. METHODS: WES was performed on 66 individuals with neurogenetic diseases using candidate gene filters and stringent algorithms for assessing sequence variants. Pathogenic or likely pathogenic missense variants were interpreted using in silico prediction tools, family segregation analysis, previous publications of disease association and relevant biological assays. RESULTS: Molecular diagnosis was achieved in 39% (n=26) including 59% of childhood-onset cases and 27% of late-onset cases. Overall, 37% (10/27) of myopathy, 41% (9/22) of neuropathy, 22% (2/9) of MND and 63% (5/8) of complex phenotypes were given genetic diagnosis. Twenty-seven disease-associated variants were identified including ten novel variants in FBXO38, LAMA2, MFN2, MYH7, PNPLA6, SH3TC2 and SPTLC1. Single-nucleotide variants (n=10) affected conserved residues within functional domains and previously identified mutation hot-spots. Established pathogenic variants (n=16) presented with atypical features, such as optic neuropathy in adult polyglucosan body disease, facial dysmorphism and skeletal anomalies in cerebrotendinous xanthomatosis, steroid-responsive weakness in congenital myasthenia syndrome 10. Potentially treatable rare diseases were diagnosed, improving the quality of life in some patients. CONCLUSIONS: Integrating deep phenotyping, gene filter algorithms and biological assays increased diagnostic yield of exome sequencing, identified novel pathogenic variants and extended phenotypes of difficult to diagnose rare neurogenetic disorders in an outpatient clinic setting.

Friedreich ataxia in a family from Mali, West Africa/Friedreich ataxia in a Malian family.

Friedreich ataxia is the most common inherited ataxia in the world, but yet to be reported in black African. We report the first genetically confirmed case in a West African family. Studying genetic diseases in populations with diverse backgrounds may give new insights into their pathophysiology for future therapeutic targets.

A high-throughput genome-wide RNAi screen identifies modifiers of survival motor neuron protein.

Spinal muscular atrophy (SMA) is a debilitating neurological disorder marked by degeneration of spinal motor neurons and muscle atrophy. SMA results from mutations in survival motor neuron 1 (SMN1), leading to deficiency of survival motor neuron (SMN) protein. Current therapies increase SMN protein and improve patient survival but have variable improvements in motor function, making it necessary to identify complementary strategies to further improve disease outcomes. Here, we perform a genome-wide RNAi screen using a luciferase-based activity reporter and identify genes involved in regulating SMN gene expression, RNA processing, and protein stability. We show that reduced expression of Transcription Export complex components increases SMN levels through the regulation of nuclear/cytoplasmic RNA transport. We also show that the E3 ligase, Neurl2, works cooperatively with Mib1 to ubiquitinate and promote SMN degradation. Together, our screen uncovers pathways through which SMN expression is regulated, potentially revealing additional strategies to treat SMA.

Targeting the 5' untranslated region of SMN2 as a therapeutic strategy for spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by mutations in the survival motor neuron 1 (SMN1) gene. All patients have at least one copy of a paralog, SMN2, but a C-to-T transition in this gene results in exon 7 skipping in a majority of transcripts. Approved treatment for SMA involves promoting exon 7 inclusion in the SMN2 transcript or increasing the amount of full-length SMN by gene replacement with a viral vector. Increasing the pool of SMN2 transcripts and increasing their translational efficiency can be used to enhance splice correction. We sought to determine whether the 5' untranslated region (5' UTR) of SMN2 contains a repressive feature that can be targeted to increase SMN levels. We found that antisense oligonucleotides (ASOs) complementary to the 5' end of SMN2 increase SMN mRNA and protein levels and that this effect is due to inhibition of SMN2 mRNA decay. Moreover, use of the 5' UTR ASO in combination with a splice-switching oligonucleotide (SSO) increases SMN levels above those attained with the SSO alone. Our results add to the current understanding of SMN regulation and point toward a new therapeutic target for SMA.

Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA).

Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular disorder caused by CAG trinucleotide expansion in the gene encoding the androgen receptor (AR). In the central nervous system, lower motor neurons are selectively affected, whereas pathology of patients and animal models also indicates involvement of skeletal muscle including loss of fast-twitch type 2 fibres and increased slow-twitch type 1 fibres, together with a glycolytic-to-oxidative metabolic switch. Evaluation of muscle and fat using MRI, in addition to biochemical indices such as serum creatinine level, are promising biomarkers to track the disease progression. The serum level of creatinine starts to decrease before the onset of muscle weakness, followed by the emergence of hand tremor, a prodromal sign of the disease. Androgen-dependent nuclear accumulation of the polyglutamine-expanded AR is an essential step in the pathogenesis, providing therapeutic opportunities via hormonal manipulation and gene silencing with antisense oligonucleotides. Animal studies also suggest that hyperactivation of Src, alteration of autophagy and a mitochondrial deficit underlie the neuromuscular degeneration in SBMA and provide alternative therapeutic targets.

Molecular pathogenesis of spinal bulbar muscular atrophy (Kennedy's disease) and avenues for treatment.

PURPOSE OF REVIEW: The aim of this study was to illustrate the current understanding and avenues for developing treatment in spinal and bulbar muscular atrophy (SBMA), an inherited neuromuscular disorder caused by a CAG trinucleotide repeat expansion in the androgen receptor (AR) gene. RECENT FINDINGS: Important advances have been made in characterizing the molecular mechanism of the disease, including the disruption of protein homeostasis, intracellular trafficking and signalling pathways. Biomarkers such as MRI quantification of muscle volume and fat fraction have been used to track disease progression, and will be useful in future clinical studies. Therapies tested and under development have been based on diverse strategies, including targeting mutant AR gene expression, stability and activity, and pathways that mitigate disease toxicity. SUMMARY: We provide an overview of the recent advances in understanding the SBMA disease mechanism and highlight efforts to translate these insights into well tolerated and effective therapy.

Linking epigenetic dysregulation, mitochondrial impairment, and metabolic dysfunction in SBMA motor neurons.

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disorder caused by a polyglutamine expansion in the androgen receptor (AR). Using gene expression analysis and ChIP sequencing, we mapped transcriptional changes in genetically engineered patient stem cell-derived motor neurons. We found that transcriptional dysregulation in SBMA can occur through AR-mediated histone modification. We detected reduced histone acetylation, along with decreased expression of genes encoding compensatory metabolic proteins and reduced substrate availability for mitochondrial function. Furthermore, we found that pyruvate supplementation corrected this deficiency and improved mitochondrial function and SBMA motor neuron viability. We propose that epigenetic dysregulation of metabolic genes contributes to reduced mitochondrial ATP production. Our results show a molecular link between altered epigenetic regulation and mitochondrial metabolism that contributes to neurodegeneration.