Spinal muscular atrophy (SMA) is a progressive motor neuron disease caused by loss or mutation of the survival motor neuron 1 (SMN1) gene and retention of SMN2. We performed targeted capture and sequencing of the SMN2, CFTR, and PLS3 genes in 217 SMA patients. We identified a 6.3 kilobase deletion that occurred in both SMN1 and SMN2 (SMN½) and removed exons 7 and 8. The deletion junction was flanked by a 21 base pair repeat that occurred 15 times in the SMN½ gene. We screened for its presence in 466 individuals with known SMN1 and SMN2 copy number. In individuals with 1 SMN1 and 0 SMN2 copies the deletion occurred in 63% of cases. We modeled the deletion junction frequency and determined that the deletion occurred in both SMN1 and SMN2. We have identified the first deletion junction where the deletion removes exons 7 and 8 of SMN½. As it occurred in SMN1 it is a pathogenic mutation. We called variants in the PLS3 and SMN2 genes and tested for association with mild or severe exception patients. The variants A-44G, A-549G and C-1897T in intron 6 of SMN2 were significantly associated with mild exception patients but no PLS3 variants correlated with severity. The variants occurred in 14 out of 58 of our mild exception patients indicating that mild exception patients with an intact SMN2 gene
ObjectiveIdentifying simple biomarkers that can predict or track disease progression in patients with spinal muscular atrophy (SMA) remains an unmet clinical need. To test the hypothesis that serum creatinine (Crn) could be a prognostic biomarker for monitoring progression of denervation in patients with SMA, we determined whether serum Crn concentration correlates with disease severity in patients with SMA.MethodsWe examined a cohort of 238 patients with SMA with 1,130 Crn observations between 2000 and 2016. Analyses were corrected for age, and 156 patients with SMA had dual-energy x-ray absorptiometry data available for correction for lean mass. We investigated the relationship between Crn and SMA type, survival motor neuron 2 (SMN2) copies, and Hammersmith Functional Motor Scale (HFMS) score as primary outcomes. In addition, we tested for associations between Crn and maximum ulnar compound muscle action potential amplitude (CMAP) and motor unit number estimation (MUNE).ResultsPatients with SMA type 3 had 2.2-fold (95% confidence interval [CI] 1.93–2.49; p < 0.0001) higher Crn levels compared to those with SMA type 1 and 1.7-fold (95% CI 1.52–1.82; p < 0.0001) higher Crn levels compared to patients with SMA type 2. Patients with SMA type 2 had 1.4-fold (95% CI 1.31–1.58; p < 0.0001) higher Crn levels than patients with SMA type 1. Patients with SMA with 4 SMN2 copies had 1.8-fold (95% CI 1.57–2.11; p < 0.0001) higher Crn levels compared to patients with SMA with 2 SMN2 copies and 1.4-fold (95% CI 1.24–1.58; p < 0.0001) higher Crn levels compared to patients with SMA with 3 SMN2 copies. Patients with SMA with 3 SMN2 copies had 1.4-fold (95% CI 1.21–1.56; p < 0.0001) higher Crn levels than patients with SMA with 2 SMN2 copies. Mixed-effect model revealed significant differences in Crn levels among walkers, sitters, and nonsitters (p < 0.0001) and positive associations between Crn and maximum CMAP (p < 0.0001) and between Crn and MUNE (p < 0.0001). After correction for lean mass, there were still significant associations between Crn and SMA type, SMN2 copies, HFMS, CMAP, and MUNE.ConclusionsThese findings indicate that decreased Crn levels reflect disease severity, suggesting that Crn is a candidate biomarker for SMA progression. We conclude that Crn measurements should be included in the routine analysis of all patients with SMA. In future studies, it will be important to determine whether Crn levels respond to molecular and gene therapies.
Introduction We sought to determine whether survival motor neuron (SMN) protein blood levels correlate with denervation and SMN2 copies in spinal muscular atrophy (SMA). Methods Using a mixed‐effect model, we tested associations between SMN levels, compound muscle action potential (CMAP), and SMN2 copies in a cohort of 74 patients with SMA. We analyzed a subset of 19 of these patients plus four additional patients who had been treated with received gene therapy to examine SMN trajectories early in life. Results Patients with SMA who had lower CMAP values had lower circulating SMN levels ( P = .04). Survival motor neuron protein levels were different between patients with two and three SMN2 copies ( P < .0001) and between symptomatic and presymptomatic patients ( P < .0001), with the highest levels after birth and progressive decline over the first 3 years. Neither nusinersen nor gene therapy clearly altered SMN levels. Discussion These data provide evidence that whole blood SMN levels correlate with SMN2 copy number and severity of denervation.
ObjectiveTo determine changes in serum profiles and kidney tissues from patients with spinal muscular atrophy (SMA) type 1 compared with age- and sex-matched controls.MethodsIn this cohort study, we investigated renal structure and function in infants and children with SMA type 1 in comparison with age- and sex-matched controls.ResultsPatients with SMA had alterations in serum creatinine, cystatin C, sodium, glucose, and calcium concentrations, granular casts and crystals in urine, and nephrocalcinosis and fibrosis. Nephrotoxicity and polycystic kidney disease PCR arrays revealed multiple differentially expressed genes, and immunoblot analysis showed decreased calcium-sensing receptors and calbindin and increased insulin-like growth factor–binding proteins in kidneys from patients with SMA.ConclusionsThese findings demonstrate that patients with SMA type 1, in the absence of disease-modifying therapies, frequently manifest impaired renal function as a primary or secondary consequence of their disease. This study provides new insights into systemic contributions to SMA disease pathogenesis and the need to identify coadjuvant therapies.
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