Neuropathy due to bi-allelic SH3TC2 variants: genotype-phenotype correlation and natural history.

Recessive SH3TC2 variants cause Charcot-Marie-Tooth disease type 4C (CMT4C). CMT4C is typically a sensorimotor demyelinating polyneuropathy, marked by early onset spinal deformities, but its clinical characteristics and severity are quite variable. Clear relationships between pathogenic variants and the spectrum of disease manifestations are to date lacking. Gene replacement therapy has been shown to ameliorate the phenotype in a mouse model of CMT4C, emphasizing the need for natural history studies to inform clinical trial readiness. Data, including both genetic information and clinical characteristics, were compiled from the longitudinal, prospective dataset of the Inherited Neuropathy Consortium, a member of the Rare Diseases Clinical Research Network (INC-RDCRN). The Charcot Marie Tooth Neuropathy Score (CMTNS), Examination Score (CMTES) and the Rasch-weighted CMTES (CMTES-R) were used to describe symptoms, neurological examinations and neurophysiological characteristics. Standardized response means were calculated at yearly intervals and a mixed model for repeated measures was used to estimate the change in CMTES and CMTES-R over time. Fifty-six individuals (59% female), median age 27 years (range 2-67 years) with homozygous or compound heterozygous variants in SH3TC2 were identified, including 34 unique variants, 14 of which have not previously been published. Twenty-eight participants had longitudinal data available. While there was no significant difference in the CMTES in those with protein truncating versus non-protein truncating variants, there were significant differences in the mean ulnar nerve compound muscle action potential amplitude, the mean radial sensory nerve action potential amplitude, and in the prevalence of scoliosis, suggesting the possibility of a milder phenotype in individuals with one or two non-protein-truncating variants. Overall, the mean value of the CMTES was 13, reflecting moderate clinical severity. There was a high rate of scoliosis (81%), scoliosis surgery (36%), and walking difficulty (94%) among study participants. The CMTES and CMTES-R appeared moderately responsive to change over extended follow-up, demonstrating a standardized response mean of 0.81 standard deviation units or 0.71 standard deviation units, respectively, over 3 years. Our analysis represents the largest cross-sectional and only longitudinal study to date, of the clinical phenotype of both adults and children with CMT4C. With the promise of upcoming genetic treatments, these data will further define the natural history of the disease and inform study design in preparation for clinical trials.

Newborn Screening for Spinal Muscular Atrophy in New York State: Clinical Outcomes From the First 3 Years.

BACKGROUND AND OBJECTIVES: Spinal muscular atrophy (SMA) was added to the Recommended Uniform Screening Panel (RUSP) in July 2018, largely on the basis of the availability and efficacy of newly-approved disease modifying therapies. New York State (NYS) started universal newborn screening for SMA in October 2018. The authors report the findings from the first 3 years of screening. METHODS: Statewide neonatal screening was conducted using DNA extracted from dried blood spots using a real-time quantitative polymerase chain reaction (qPCR) assay. Retrospective follow-up data were collected from 9 referral centers across the state on 34 infants. RESULTS: In the first three years since statewide implementation, nearly 650,000 infants have been screened for SMA. 34 babies screened positive and were referred to a neuromuscular specialty care center. The incidence remains lower than previously predicted. The majority (94%), including all infants with 2-3 copies of SMN2, have received treatment. Among treated infants, the overwhelming majority (97%; 29/30) have received gene replacement. All infants in this cohort with 3 copies of SMN2 are clinically asymptomatic post-treatment based on early clinical follow-up data. Infants with 2 copies of SMN2 are more variable in their outcomes. Electrodiagnostic outcomes data from a subgroup of patients (n=11) for whom pre- and post-treatment data demonstrated either improvement or no change in CMAP amplitude at last clinical follow-up compared to pre-treatment baseline. Most infants were treated before 6 weeks of age (median = 34.5 DOL; range 11-180). Delays and barriers to treatment identified by treating clinicians followed two broad themes: medical and non-medical. Medical delays most commonly reported were presence of AAV9 antibodies and elevated troponin I levels. Non-medical barriers included delays in obtaining insurance as well as insurance policies regarding specific treatment modalities. DISCUSSION: The findings from the NYS cohort of newborn screen-identified infants are consistent with other reports of improved outcomes from early diagnosis and treatment. Additional biomarkers of motor neuron health including electromyography can potentially be helpful in detecting pre-clinical decline.

Implementation of population-based newborn screening reveals low incidence of spinal muscular atrophy.

PURPOSE: Spinal muscular atrophy (SMA) was added to the Recommended Uniform Screening Panel (RUSP) in July 2018, following FDA approval of the first effective SMA treatment, and demonstration of feasibility of high-throughput newborn screening using a primary molecular assay. SMA newborn screening was implemented in New York State (NYS) on 1 October 2018. METHODS: Screening was conducted using DNA extracted from dried blood spots with a multiplex real-time quantitative polymerase chain reaction (qPCR) assay targeting the recurrent SMN1 exon 7 gene deletion. RESULTS: During the first year, 225,093 infants were tested. Eight screened positive, were referred for follow-up, and confirmed to be homozygous for the deletion. Infants with two or three copies of the SMN2 gene, predicting more severe, earlier-onset SMA, were treated with antisense oligonucleotide and/or gene therapy. One infant with ≥4 copies SMN2 also received gene therapy. CONCLUSION: Newborn screening permits presymptomatic SMA diagnosis, when treatment initiation is most beneficial. At 1 in 28,137 (95% confidence interval [CI]: 1 in 14,259 to 55,525), the NYS SMA incidence is 2.6- to 4.7-fold lower than expected. The low SMA incidence is likely attributable to imprecise and biased estimates, coupled with increased awareness, access to and uptake of carrier screening, genetic counseling, cascade testing, prenatal diagnosis, and advanced reproductive technologies.