Intrathecal Gene Therapy for Giant Axonal Neuropathy.

BACKGROUND: Giant axonal neuropathy is a rare, autosomal recessive, pediatric, polysymptomatic, neurodegenerative disorder caused by biallelic loss-of-function variants in GAN, the gene encoding gigaxonin. METHODS: We conducted an intrathecal dose-escalation study of scAAV9/JeT-GAN (a self-complementary adeno-associated virus-based gene therapy containing the GAN transgene) in children with giant axonal neuropathy. Safety was the primary end point. The key secondary clinical end point was at least a 95% posterior probability of slowing the rate of change (i.e., slope) in the 32-item Motor Function Measure total percent score at 1 year after treatment, as compared with the pretreatment slope. RESULTS: One of four intrathecal doses of scAAV9/JeT-GAN was administered to 14 participants - 3.5×1013 total vector genomes (vg) (in 2 participants), 1.2×1014 vg (in 4), 1.8×1014 vg (in 5), and 3.5×1014 vg (in 3). During a median observation period of 68.7 months (range, 8.6 to 90.5), of 48 serious adverse events that had occurred, 1 (fever) was possibly related to treatment; 129 of 682 adverse events were possibly related to treatment. The mean pretreatment slope in the total cohort was -7.17 percentage points per year (95% credible interval, -8.36 to -5.97). At 1 year after treatment, posterior mean changes in slope were -0.54 percentage points (95% credible interval, -7.48 to 6.28) with the 3.5×1013-vg dose, 3.23 percentage points (95% credible interval, -1.27 to 7.65) with the 1.2×1014-vg dose, 5.32 percentage points (95% credible interval, 1.07 to 9.57) with the 1.8×1014-vg dose, and 3.43 percentage points (95% credible interval, -1.89 to 8.82) with the 3.5×1014-vg dose. The corresponding posterior probabilities for slowing the slope were 44% (95% credible interval, 43 to 44); 92% (95% credible interval, 92 to 93); 99% (95% credible interval, 99 to 99), which was above the efficacy threshold; and 90% (95% credible interval, 89 to 90). Between 6 and 24 months after gene transfer, sensory-nerve action potential amplitudes increased, stopped declining, or became recordable after being absent in 6 participants but remained absent in 8. CONCLUSIONS: Intrathecal gene transfer with scAAV9/JeT-GAN for giant axonal neuropathy was associated with adverse events and resulted in a possible benefit in motor function scores and other measures at some vector doses over a year. Further studies are warranted to determine the safety and efficacy of intrathecal AAV-mediated gene therapy in this disorder. (Funded by the National Institute of Neurological Disorders and Stroke and others; ClinicalTrials.gov number, NCT02362438.).

TRPV4 neuromuscular disease registry highlights bulbar, skeletal and proximal limb manifestations.

Dominant missense mutations of the calcium-permeable cation channel TRPV4 cause Charcot-Marie-Tooth disease (CMT) type 2C and two forms of distal spinal muscular atrophy. These conditions are collectively referred to as TRPV4-related neuromuscular disease and share features of motor greater than sensory dysfunction and frequent vocal fold weakness. Pathogenic variants lead to gain of ion channel function that can be rescued by TRPV4 antagonists in cellular and animal models. As small molecule TRPV4 antagonists have proven safe in trials for other disease indications, channel inhibition is a promising therapeutic strategy for TRPV4 patients. However, the current knowledge of the clinical features and natural history of TRPV4-related neuromuscular disease is insufficient to enable rational clinical trial design. To address these issues, we developed a TRPV4 patient database and administered a TRPV4-specific patient questionnaire. Here, we report demographic and clinical information, including CMT examination scores (CMTES), from 68 patients with known pathogenic TRPV4 variants, 40 of whom also completed the TRPV4 patient questionnaire. TRPV4 patients showed a bimodal age of onset, with the largest peak occurring in the first 2 years of life. Compared to CMT1A patients, TRPV4 patients showed distinct symptoms and signs, manifesting more ambulatory difficulties and more frequent involvement of proximal arm and leg muscles. Although patients reported fewer sensory symptoms, sensory dysfunction was often detected clinically. Many patients were affected by vocal fold weakness (55%) and shortness of breath (55%), and 11% required ventilatory support. Skeletal abnormalities were common, including scoliosis (64%), arthrogryposis (33%), and foot deformities. Strikingly, patients with infantile onset of disease showed less sensory involvement and less progression of symptoms. These results highlight distinctive clinical features in TRPV4 patients, including motor-predominant disease, proximal arm and leg weakness, severe ambulatory difficulties, vocal fold weakness, respiratory dysfunction, and skeletal involvement. In addition, patients with infantile onset of disease appeared to have a distinct phenotype with less apparent disease progression based on CMTES. These collective observations indicate that clinical trial design for TRPV4-related neuromuscular disease should include outcome measures that reliably capture non-length dependent motor dysfunction, vocal fold weakness, and respiratory disease.

Combined clinical, structural, and cellular studies discriminate pathogenic and benign TRPV4 variants.

Dominant mutations in the calcium-permeable ion channel TRPV4 (transient receptor potential vanilloid 4) cause diverse and largely distinct channelopathies, including inherited forms of neuromuscular disease, skeletal dysplasias, and arthropathy. Pathogenic TRPV4 mutations cause gain of ion channel function and toxicity that can be rescued by small molecule TRPV4 antagonists in cellular and animal models, suggesting that TRPV4 antagonism could be therapeutic for patients. Numerous variants in TRPV4 have been detected with targeted and whole exome/genome sequencing, but for the vast majority, their pathogenicity remains unclear. Here, we used a combination of clinical information and experimental structure-function analyses to evaluate 30 TRPV4 variants across various functional protein domains. We report clinical features of seven patients with TRPV4 variants of unknown significance and provide extensive functional characterization of these and an additional 17 variants, including structural position, ion channel function, subcellular localization, expression level, cytotoxicity, and protein-protein interactions. We find that gain-of-function mutations within the TRPV4 intracellular ankyrin repeat domain target charged amino acid residues important for RhoA interaction, whereas ankyrin repeat domain residues outside of the RhoA interface have normal or reduced ion channel activity. We further identify a cluster of gain-of-function variants within the intracellular intrinsically disordered region that may cause toxicity via altered interactions with membrane lipids. In contrast, assessed variants in the transmembrane domain and other regions of the intrinsically disordered region do not cause gain of function and are likely benign. Clinical features associated with gain of function and cytotoxicity include congenital onset of disease, vocal cord weakness, and motor predominant disease, whereas patients with likely benign variants often demonstrated late-onset and sensory-predominant disease. These results provide a framework for assessing additional TRPV4 variants with respect to likely pathogenicity, which will yield critical information to inform patient selection for future clinical trials for TRPV4 channelopathies.

Continued benefit of nusinersen initiated in the presymptomatic stage of spinal muscular atrophy: 5-year update of the NURTURE study.

INTRODUCTION/AIMS: NURTURE (NCT02386553) is an open-label study of nusinersen in children (two SMN2 copies, n = 15; three SMN2 copies, n = 10) who initiated treatment in the presymptomatic stage of spinal muscular atrophy (SMA). A prior analysis after ~3 y showed benefits on survival, respiratory outcomes, motor milestone achievement, and a favorable safety profile. An additional 2 y of follow-up (data cut: February 15, 2021) are reported. METHODS: The primary endpoint is time to death or respiratory intervention (≥6 h/day continuously for ≥7 days or tracheostomy). Secondary outcomes include overall survival, motor function, and safety. RESULTS: Median age of children was 4.9 (3.8-5.5) y at last visit. No children have discontinued the study or treatment. All were alive. No additional children utilized respiratory intervention (defined per primary endpoint) since the prior data cut. Children with three SMN2 copies achieved all World Health Organization (WHO) motor milestones, with all but one milestone in one child within normal developmental timeframes. All 15 children with two SMN2 copies achieved sitting without support, 14/15 walking with assistance, and 13/15 walking alone. Mean Hammersmith Functional Motor Scale Expanded total scores showed continued improvement. Subgroups with two SMN2 copies, minimum baseline compound muscle action potential amplitude ≥2 mV, and no baseline areflexia had better motor and nonmotor outcomes versus all children with two SMN2 copies. DISCUSSION: These results demonstrate the value of early treatment, durability of treatment effect, and favorable safety profile after ~5 y of nusinersen treatment. Inclusion/exclusion criteria and baseline characteristics should be considered when interpreting presymptomatic SMA trial data.

Clinical and genetic spectrum of a large cohort of patients with δ-sarcoglycan muscular dystrophy.

Sarcoglycanopathies include four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. Delta-sarcoglycanopathy (LGMDR6) is the least frequent and is considered an ultra-rare disease. Our aim was to characterize the clinical and genetic spectrum of a large international cohort of LGMDR6 patients and to investigate whether or not genetic or protein expression data could predict a disease's severity. This is a retrospective study collecting demographic, genetic, clinical and histological data of patients with genetically confirmed LGMDR6 including protein expression data from muscle biopsies. We contacted 128 paediatric and adult neuromuscular units around the world that reviewed genetic data of patients with a clinical diagnosis of a neuromuscular disorder. We identified 30 patients with a confirmed diagnosis of LGMDR6 of which 23 patients were included in this study. Eighty-seven per cent of the patients had consanguineous parents. Ninety-one per cent of the patients were symptomatic at the time of the analysis. Proximal muscle weakness of the upper and lower limbs was the most common presenting symptom. Distal muscle weakness was observed early over the course of the disease in 56.5% of the patients. Cardiac involvement was reported in five patients (21.7%) and four patients (17.4%) required non-invasive ventilation. Sixty per cent of patients were wheelchair-bound since early teens (median age of 12.0 years). Patients with absent expression of the sarcoglycan complex on muscle biopsy had a significant earlier onset of symptoms and an earlier age of loss of ambulation compared to patients with residual protein expression. This study confirmed that delta-sarcoglycanopathy is an ultra-rare neuromuscular condition and described the clinical and molecular characteristics of the largest yet-reported collected cohort of patients. Our results showed that this is a very severe and quickly progressive disease characterized by generalized muscle weakness affecting predominantly proximal and distal muscles of the limbs. Similar to other forms of sarcoglycanopathies, the severity and rate of progressive weakness correlates inversely with the abundance of protein on muscle biopsy.

Intron mutations and early transcription termination in Duchenne and Becker muscular dystrophy.

DMD pathogenic variants for Duchenne and Becker muscular dystrophy are detectable with high sensitivity by standard clinical exome analyses of genomic DNA. However, up to 7% of DMD mutations are deep intronic and analysis of muscle-derived RNA is an important diagnostic step for patients who have negative genomic testing but abnormal dystrophin expression in muscle. In this study, muscle biopsies were evaluated from 19 patients with clinical features of a dystrophinopathy, but negative clinical DMD mutation analysis. Reverse transcription-polymerase chain reaction or high-throughput RNA sequencing methods identified 19 mutations with one of three pathogenic pseudoexon types: deep intronic point mutations, deletions or insertions, and translocations. In association with point mutations creating intronic splice acceptor sites, we observed the first examples of DMD pseudo 3'-terminal exon mutations causing high efficiency transcription termination within introns. This connection between splicing and premature transcription termination is reminiscent of U1 snRNP-mediating telescripting in sustaining RNA polymerase II elongation across large genes, such as DMD. We propose a novel classification of three distinct types of mutations identifiable by muscle RNA analysis, each of which differ in potential treatment approaches. Recognition and appropriate characterization may lead to therapies directed toward full-length dystrophin expression for some patients.

Hip Pain in Patients With Spinal Muscular Atrophy: Prevalence, Intensity, Interference, and Factors Associated With Moderate to Severe Pain.

BACKGROUND: A subset of patients with spinal muscular atrophy (SMA) develop hip pain. We analyzed (1) the characteristics of hip pain in patients with SMA (prevalence, intensity, interference with activities, and responsiveness to treatment) and (2) factors (patient, clinical, and radiographic) associated with moderate to severe pain. METHODS: We performed a retrospective record review and telephone survey of 104 patients with SMA (77% response rate; 44% female; mean age, 22±13 y) who presented for treatment between 2010 and 2020. Patient, clinical, and radiographic characteristics (when available) were recorded. Patients with current or past hip pain were asked about pain characteristics. Pain intensity and interference were assessed with the Brief Pain Inventory, modified for SMA (scale, 0 to 10 with 0 indicating no pain/interference). We used univariate analysis and ordered logistic regression to determine associations between patient factors and hip pain (α=0.05). RESULTS: Hip pain occurred in 60/104 patients (58%), with 15 (14%) indicating moderate to severe pain. Compared with patients with normal body mass index values, patients who were obese had 5.4 times the odds [95% confidence interval (CI), 1.3-23] of moderate to severe pain. Hip contractures [adjusted odds ratio (aOR), 3.2; 95% CI, 1.2-8.8] and dislocations (aOR, 2.9; 95% CI, 1.1-7.9) were associated with greater odds of pain compared with hips without these presentations. Surgical correction for scoliosis (aOR, 2.6; 95% CI, 1.1-6.5) was also associated with greater odds of moderate to severe pain. Femoral head migration percentage was the only radiographic parameter associated with pain. Mean modified Brief Pain Inventory pain intensity was 2.1±2.3. Prolonged sitting, sleep, and transfers (eg, bed to wheelchair) were the activities most affected by pain. CONCLUSIONS: Hip pain was moderate to severe in 14% of patients with SMA. Obesity, hip contractures, surgical correction of scoliosis, and hip dislocations were independently associated with pain. Although mean pain intensity was low, hip pain interfered with daily activities, including prolonged sitting, sleep, and transfers. LEVEL OF EVIDENCE: Level III.

Detection of SMN1 to SMN2 gene conversion events and partial SMN1 gene deletions using array digital PCR.

Proximal spinal muscular atrophy (SMA), a leading genetic cause of infant death worldwide, is an early-onset motor neuron disease characterized by loss of α-motor neurons and associated muscle atrophy. SMA is caused by deletion or other disabling mutations of survival motor neuron 1 (SMN1) but retention of one or more copies of the paralog SMN2. Within the SMA population, there is substantial variation in SMN2 copy number (CN); in general, those individuals with SMA who have a high SMN2 CN have a milder disease. Because SMN2 functions as a disease modifier, its accurate CN determination may have clinical relevance. In this study, we describe the development of array digital PCR (dPCR) to quantify SMN1 and SMN2 CNs in DNA samples using probes that can distinguish the single nucleotide difference between SMN1 and SMN2 in exon 8. This set of dPCR assays can accurately and reliably measure the number of SMN1 and SMN2 copies in DNA samples. In a cohort of SMA patient-derived cell lines, the assay confirmed a strong inverse correlation between SMN2 CN and disease severity. We can detect SMN1-SMN2 gene conversion events in DNA samples by comparing CNs at exon 7 and exon 8. Partial deletions of SMN1 can also be detected with dPCR by comparing CNs at exon 7 or exon 8 with those at intron 1. Array dPCR is a practical technique to determine, accurately and reliably, SMN1 and SMN2 CNs from SMA samples as well as identify gene conversion events and partial deletions of SMN1.

The GENDULF algorithm: mining transcriptomics to uncover modifier genes for monogenic diseases.

Modifier genes are believed to account for the clinical variability observed in many Mendelian disorders, but their identification remains challenging due to the limited availability of genomics data from large patient cohorts. Here, we present GENDULF (GENetic moDULators identiFication), one of the first methods to facilitate prediction of disease modifiers using healthy and diseased tissue gene expression data. GENDULF is designed for monogenic diseases in which the mechanism is loss of function leading to reduced expression of the mutated gene. When applied to cystic fibrosis, GENDULF successfully identifies multiple, previously established disease modifiers, including EHF, SLC6A14, and CLCA1. It is then utilized in spinal muscular atrophy (SMA) and predicts U2AF1 as a modifier whose low expression correlates with higher SMN2 pre-mRNA exon 7 retention. Indeed, knockdown of U2AF1 in SMA patient-derived cells leads to increased full-length SMN2 transcript and SMN protein expression. Taking advantage of the increasing availability of transcriptomic data, GENDULF is a novel addition to existing strategies for prediction of genetic disease modifiers, providing insights into disease pathogenesis and uncovering novel therapeutic targets.

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.

Safety and efficacy of nusinersen in spinal muscular atrophy: The EMBRACE study.

INTRODUCTION: The EMBRACE study (Clinical Trials No. NCT02462759) evaluated nusinersen in infants/children with infantile- or later-onset spinal muscular atrophy (SMA) who were ineligible for the ENDEAR and CHERISH studies. METHODS: Participants were randomized to intrathecal nusinersen (12-mg scaled equivalent dose; n = 14) or sham procedure (n = 7) in part 1 (~14 months) and subsequently received open-label nusinersen for ~24 months in part 2 of the study. RESULTS: Part 1 was stopped early after the demonstration of motor function benefit with nusinersen in ENDEAR. There were no nusinersen-related adverse events (AEs) and no study discontinuations due to nusinersen-related AEs. The most common AEs included pyrexia, cough, pneumonia, and upper respiratory tract infections. Motor milestone responder rates were higher in those receiving nusinersen at last available assessment (93%) than in those receiving sham procedure in part 1 (29%) or transitioned from sham to nusinersen in part 2 (83%). This functional improvement was observed despite the small sample size and shortened part 1 trial duration that undermined the power of the study to demonstrate such treatment effects at a significant level. DISCUSSION: Nusinersen demonstrated a favorable long-term benefit-risk profile in this broad population of individuals with infantile- or later-onset SMA.

Retrospective Diagnosis of Ataxia-Telangiectasia in an Adolescent Patient With a Remote History of T-Cell Leukemia.

Ataxia-telangiectasia (A-T) is a rare autosomal recessive disorder characterized by progressive cerebellar degeneration that is typically diagnosed in early childhood. A-T is associated with a predisposition to malignancies, particularly lymphoid tumors in childhood and early adulthood. An adolescent girl with minimal neurologic symptoms was diagnosed with A-T 8 years after completing therapy for T-cell acute lymphoblastic leukemia, following a diagnosis of ATM-mutated breast cancer in her mother. We highlight the importance of recognizing ATM mutations in T-cell acute lymphoblastic leukemia, appreciating the phenotypic heterogeneity of A-T, and defining optimal cancer screening in A-T patients.

Charcot-Marie-Tooth Disease type 4C: Novel mutations, clinical presentations, and diagnostic challenges.

INTRODUCTION: This study analyzes and describes atypical presentations of Charcot-Marie-Tooth disease type 4C (CMT4C). METHODS: We present clinical and physiologic features of 5 patients with CMT4C caused by biallelic private mutations of SH3TC2. RESULTS: All patients manifested scoliosis, and nerve conduction study indicated results in the demyelinating range. All patients exhibited signs of motor impairment within the first years of life. We describe 2 or more different genetic diseases in the same patient, atypical presentations of CMT, and 3 new mutations in CMT4C patients. DISCUSSION: A new era of unbiased genetic testing has led to this small case series of individuals with CMT4C and highlights the recognition of different genetic diseases in CMT4C patients for accurate diagnosis, genetic risk identification, and therapeutic intervention. The phenotype of CMT4C, in addition, appears to be enriched by a number of features unusual for the broad CMT category. Muscle Nerve 57: 749-755, 2018.

Clinical trial of L-Carnitine and valproic acid in spinal muscular atrophy type I.

INTRODUCTION: The aim of this study was to determine the safety and therapeutic potential of L-carnitine and valproic acid (VPA) in infants with spinal muscular atrophy (SMA). METHODS: Our investigation was an open-label phase 2 multicenter trial of L-carnitine and VPA in infants with SMA type I with retrospective comparison to an untreated, matched cohort. Primary outcomes were: safety and adverse events; secondary outcomes were survival, time to death/>16 hours/day of ventilator support; motor outcomes; and maximum ulnar compound motor action potential amplitude. RESULTS: A total of 245 AEs were observed in 35 of the 37 treated subjects (95%). Respiratory events accounted for 49% of all adverse events, resulting in 14 deaths. Survival was not significantly different between treated and untreated cohorts. DISCUSSION: This trial provides evidence that, in infants with SMA type I, L-carnitine/VPA is ineffective at altering survival. The substantial proportion of infants reaching end-points within 6 months of enrollment underscores the urgent need for pre-symptomatic treatment in SMA type I. Muscle Nerve 57: 193-199, 2018.

Astrocytes influence the severity of spinal muscular atrophy.

Systemically low levels of survival motor neuron-1 (SMN1) protein cause spinal muscular atrophy (SMA). α-Motor neurons of the spinal cord are considered particularly vulnerable in this genetic disorder and their dysfunction and loss cause progressive muscle weakness, paralysis and eventually premature death of afflicted individuals. Historically, SMA was therefore considered a motor neuron-autonomous disease. However, depletion of SMN in motor neurons of normal mice elicited only a very mild phenotype. Conversely, restoration of SMN to motor neurons in an SMA mouse model had only modest effects on the SMA phenotype and survival. Collectively, these results suggested that additional cell types contribute to the pathogenesis of SMA, and understanding the non-autonomous requirements is crucial for developing effective therapies. Astrocytes are critical for regulating synapse formation and function as well as metabolic support for neurons. We hypothesized that astrocyte functions are disrupted in SMA, exacerbating disease progression. Using viral-based restoration of SMN specifically to astrocytes, survival in severe and intermediate SMA mice was observed. In addition, neuromuscular circuitry was improved. Astrogliosis was prominent in end-stage SMA mice and in post-mortem patient spinal cords. Increased expression of proinflammatory cytokines was partially normalized in treated mice, suggesting that astrocytes contribute to the pathogenesis of SMA.

KIF5A mutations cause an infantile onset phenotype including severe myoclonus with evidence of mitochondrial dysfunction.

Missense mutations in kinesin family member 5A (KIF5A) cause spastic paraplegia 10. We report on 2 patients with de novo stop-loss frameshift variants in KIF5A resulting in a novel phenotype that includes severe infantile onset myoclonus, hypotonia, optic nerve abnormalities, dysphagia, apnea, and early developmental arrest. We propose that alteration and elongation of the carboxy-terminus of the protein has a dominant-negative effect, causing mitochondrial dysfunction in the setting of an abnormal kinesin "motor." These results highlight the role of expanded testing and whole-exome sequencing in critically ill infants and emphasize the importance of accurate test interpretation. Ann Neurol 2016;80:633-637.

Non-aggregating tau phosphorylation by cyclin-dependent kinase 5 contributes to motor neuron degeneration in spinal muscular atrophy.

Mechanisms underlying motor neuron degeneration in spinal muscular atrophy (SMA), the leading inherited cause of infant mortality, remain largely unknown. Many studies have established the importance of hyperphosphorylation of the microtubule-associated protein tau in various neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. However, tau phosphorylation in SMA pathogenesis has yet to be investigated. Here we show that tau phosphorylation on serine 202 (S202) and threonine 205 (T205) is increased significantly in SMA motor neurons using two SMA mouse models and human SMA patient spinal cord samples. Interestingly, phosphorylated tau does not form aggregates in motor neurons or neuromuscular junctions (NMJs), even at late stages of SMA disease, distinguishing it from other tauopathies. Hyperphosphorylation of tau on S202 and T205 is mediated by cyclin-dependent kinase 5 (Cdk5) in SMA disease condition, because tau phosphorylation at these sites is significantly reduced in Cdk5 knock-out mice; genetic knock-out of Cdk5 activating subunit p35 in an SMA mouse model also leads to reduced tau phosphorylation on S202 and T205 in the SMA;p35(-/-) compound mutant mice. In addition, expression of the phosphorylation-deficient tauS202A,T205A mutant alleviates motor neuron defects in a zebrafish SMA model in vivo and mouse motor neuron degeneration in culture, whereas expression of phosphorylation-mimetic tauS202E,T205E promotes motor neuron defects. More importantly, genetic knock-out of tau in SMA mice rescues synapse stripping on motor neurons, NMJ denervation, and motor neuron degeneration in vivo. Altogether, our findings suggest a novel mechanism for SMA pathogenesis in which hyperphosphorylation of non-aggregating tau by Cdk5 contributes to motor neuron degeneration.

Assessment of impaired coordination between respiration and deglutition in children and young adults with ataxia telangiectasia.

AIM: This cross-sectional investigation aimed to assess the value of non-invasive measures of temporal respiratory-swallow coupling in individuals with ataxic swallowing. METHOD: Twenty participants (11 males, 9 females; range 9-21y) with ataxia telangiectasia were presented with water and pudding boluses. Their 193 swallows were compared with 2200 swallows from 82 age-matched healthy controls. The two components of airway protection during swallowing that were analyzed were: direction of peri-deglutitive airflow and duration of deglutitive inhibition of respiratory airflow (DIORA). RESULTS: Safe expiratory patterns of peri-deglutitive airflow occurred significantly less often in participants with ataxia telangiectasia than in age-matched control participants (younger p<0.015 and older p<0.001). The frequency of an expiratory pattern of peri-deglutitive airflow increased with age in participants in the comparison group (p=0.006), but not in those with ataxia telangiectasia (p=0.234). With age, mean duration of DIORA decreased in controls (p<0.001) but was unchanged in participants with ataxia telangiectasia (p=0.164). INTERPRETATION: Non-invasive quantitative measures of respiratory-swallow coupling capture temporal relationships that plausibly contribute to airway compromise from dysphagia. Changes in respiratory-swallow coupling observed with advancing age in control participants were not seen in participants with ataxia telangiectasia. Measures of perturbations may herald swallowing problems prior to development of pulmonary and nutritional sequelae.

Mosaicism for dominant collagen 6 mutations as a cause for intrafamilial phenotypic variability.

Collagen 6-related dystrophies and myopathies (COL6-RD) are a group of disorders that form a wide phenotypic spectrum, ranging from severe Ullrich congenital muscular dystrophy, intermediate phenotypes, to the milder Bethlem myopathy. Both inter- and intrafamilial variable expressivity are commonly observed. We present clinical, immunohistochemical, and genetic data on four COL6-RD families with marked intergenerational phenotypic heterogeneity. This variable expression seemingly masquerades as anticipation is due to parental mosaicism for a dominant mutation, with subsequent full inheritance and penetrance of the mutation in the heterozygous offspring. We also present an additional fifth simplex patient identified as a mosaic carrier. Parental mosaicism was confirmed in the four families through quantitative analysis of the ratio of mutant versus wild-type allele (COL6A1, COL6A2, and COL6A3) in genomic DNA from various tissues, including blood, dermal fibroblasts, and saliva. Consistent with somatic mosaicism, parental samples had lower ratios of mutant versus wild-type allele compared with the fully heterozygote offspring. However, there was notable variability of the mutant allele levels between tissues tested, ranging from 16% (saliva) to 43% (fibroblasts) in one mosaic father. This is the first report demonstrating mosaicism as a cause of intrafamilial/intergenerational variability of COL6-RD, and suggests that sporadic and parental mosaicism may be more common than previously suspected.

Brain glucose metabolism in adults with ataxia-telangiectasia and their asymptomatic relatives.

Ataxia-telangiectasia is a recessive genetic disorder (ATM is the mutated gene) of childhood with severe motor impairments and whereas homozygotes manifest the disorder, heterozygotes are asymptomatic. Structural brain imaging and post-mortem studies in individuals with ataxia-telangiectasia have reported cerebellar atrophy; but abnormalities of motor control characteristic of extrapyramidal dysfunction suggest impairment of broader motor networks. Here, we investigated possible dysfunction in other brain areas in individuals with ataxia-telangiectasia and tested for brain changes in asymptomatic relatives to assess if heterozygocity affects brain function. We used positron emission tomography and (18)F-fluorodeoxyglucose to measure brain glucose metabolism (quantified as µmol/100 g/min), which serves as a marker of brain function, in 10 adults with ataxia-telangiectasia, 19 non-affected adult relatives (12 siblings, seven parents) and 29 age-matched healthy controls. Statistical parametric mapping and region of interest analyses were used to compare individuals with ataxia-telangiectasia, asymptomatic relatives, and unrelated controls. We found that participants with ataxia-telangiectasia had lower metabolism in cerebellar hemispheres (14%, P < 0.001), anterior vermis (40%, P < 0.001) and fusiform gyrus (20%, P < 0.001) compared with controls or siblings, and lower metabolism in hippocampus (12%, P = 0.05) compared with controls, and showed significant intersubject variability (decreases in vermis ranged from 18% to 60%). Participants with ataxia-telangiectasia also had higher metabolism in globus pallidus (16%, P = 0.05), which correlated negatively with motor performance. Asymptomatic relatives had lower metabolism in anterior vermis (12%; P = 0.01) and hippocampus (19%; P = 0.002) than controls. Our results indicate that, in addition to the expected decrease in cerebellar metabolism, participants with ataxia-telangiectasia had widespread changes in metabolic rates including hyperactivity in globus pallidus indicative of basal ganglia involvement. Changes in basal ganglia metabolism offer potential insight into targeting strategies for therapeutic deep brain stimulation. Our finding of decreased metabolism in vermis and hippocampus of asymptomatic relatives suggests that heterozygocity influences the function of these brain regions.