Two Japanese Patients With SMA Type 1 Suggest that Axonal-SMN May Not Modify the Disease Severity

Yamada, Hiroyuki; Nishida, Yoshihiro; Maihara, Toshiro; Sa’adah, Nihayatus; Harahap, Nur Imma Fatimah; Nurputra, Dian Kesumapramudya; Rochmah, Mawaddah Ar; Nishimura, Noriyuki; Saitô, Toshio; Kubo, Yohei; Saito, Kayoko; Nishio, Hisahide

doi:10.1016/j.pediatrneurol.2015.02.023

Cited by 5 publications

(7 citation statements)

References 12 publications

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“…Mutations in the highly conserved C-terminal domain, YG Box and QNQKE motif, hampered SMN self-oligomerization and cytoplasmic localization, and destabilize SMN protein resulting in a severe phenotype [22,33,34]. In our database, missense mutations in Cases 4 and 7 disrupted the YG Box [8,23], whereas frameshift or splicing anomaly mutations in Cases 3, 12 and 13 disrupted both the YG Box and QNQKE motif [21,22].…”

Section: Contribution Of the Intragenic Smn1 Mutations To Sma Phenotypesmentioning

confidence: 89%

“…To elucidate the relationship between clinical phenotypes of SMA patients with an intragenic SMN1 mutation and their SMN2 copy numbers, we combined the data of 7 patients reported previously [8,13,[21][22][23]] and 6 patients who were newly diagnosed as carrying an intragenic SMN1 mutation. The new patients were clinically diagnosed as having SMA type 1.…”

Section: Patientsmentioning

confidence: 99%

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Phenotypes of SMA patients retaining SMN1 with intragenic mutation

Wijaya

Rohmah

Niba

et al. 2021

Brain and Development

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Background: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by homozygous deletion or intragenic mutation of the SMN1 gene. It is well-known that high copy number of its homologous gene, SMN2, modifies the phenotype of SMN1-deleted patients. However, in the patients with intragenic SMN1 mutation, the relationship between phenotype and SMN2 copy number remains unclear.Methods: We have analyzed a total of 515 Japanese patients with SMA-like symptoms (delayed developmental milestones, respiratory failures, muscle weakness etc.) from 1996 to 2019. SMN1 and SMN2 copy numbers were determined by quantitative polymerase chain reaction (PCR) method and/or multiplex ligation-dependent probe amplification (MLPA) method. Intragenic SMN1 mutations were identified through DNA and RNA analysis of the fresh blood samples.Results: A total of 241 patients were diagnosed as having SMA. The majority of SMA patients showed complete loss of SMN1 (n = 228, 95%), but some patients retained SMN1 and carried an intragenic mutation in the retaining SMN1 (n = 13, 5%). Ten different mutations were identified in these 13 patients, consisting of missense, nonsense, frameshift and splicing defect-causing mutations. The ten mutations were c.275G > C (p.Trp92Ser), c.819_820insT (p.Thr274Tyrfs*32), c.830A > G (p.Tyr277Cys), c.5C > T (p.Ala2Val), c.826 T > C (p.Tyr276His), c.79C > T (p.Gln27*), c.188C > A (p.Ser63*), c.422 T > C (p.Leu141Pro), c.835-2A > G (exon 7 skipping) and c.835-3C > A (exon 7 skipping). It should be noted here that some patients with milder phenotype carried only a single SMN2 copy (n = 3), while other patients with severe phenotype carried 3 SMN2 copies (n = 4).Conclusion: Intragenic mutations in SMN1 may contribute more significantly to clinical severity than SMN2 copy numbers.

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Section: Contribution Of the Intragenic Smn1 Mutations To Sma Phenotypesmentioning

confidence: 89%

Section: Patientsmentioning

confidence: 99%

Phenotypes of SMA patients retaining SMN1 with intragenic mutation

Wijaya

Rohmah

Niba

et al. 2021

Brain and Development

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“…First, the cell mechanisms set in motion by a-SMN are not clarified. Second, the link between a-SMN and SMA is uncertain [ 32 ], even if the disruption of the a-SMN axonogenic properties by SMA mutations might suggest a role in SMA pathogenesis [ 14 ]. Finally, it is not as yet clear whether a-SMN might act in concert with FL-SMN, even if the potential mediators of a-SMN biological activity in axon growth and cell motility, i.e., the CCL2 and CCL7 chemokines and the growth factor IGF1, might indicate a cell role of a-SMN distinct from that of FL-SMN [ 33 ].…”

Section: Introductionmentioning

confidence: 99%

Different Stability and Proteasome-Mediated Degradation Rate of SMN Protein Isoforms

et al. 2015

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The key pathogenic steps leading to spinal muscular atrophy (SMA), a genetic disease characterized by selective motor neuron degeneration, are not fully clarified. The full-length SMN protein (FL-SMN), the main protein product of the disease gene SMN1, plays an established role in the cytoplasm in snRNP biogenesis ultimately leading to mRNA splicing within the nucleus. It is also involved in the mRNA axonal transport. However, to what extent the impairment of these two SMN functions contributes to SMA pathogenesis remains unknown. A shorter SMN isoform, axonal-SMN or a-SMN, with more specific axonal localization, has been discovered, but whether it might act in concert with FL-SMN in SMA pathogenesis is not known. As a first step in defining common or divergent intracellular roles of FL-SMN vs a-SMN proteins, we here characterized the turn-over of both proteins and investigated which pathway contributed to a-SMN degradation. We performed real time western blot and confocal immunofluorescence analysis in easily controllable in vitro settings. We analyzed co-transfected NSC34 and HeLa cells and cell clones stably expressing both a-SMN and FL-SMN proteins after specific blocking of transcript or protein synthesis and inhibition of known intracellular degradation pathways. Our data indicated that whereas the stability of both FL-SMN and a-SMN transcripts was comparable, the a-SMN protein was characterized by a much shorter half-life than FL-SMN. In addition, as already demonstrated for FL-SMN, the Ub/proteasome pathway played a major role in the a-SMN protein degradation. We hypothesize that the faster degradation rate of a-SMN vs FL-SMN is related to the protection provided by the protein complex in which FL-SMN is assembled. The diverse a-SMN vs FL-SMN C-terminus may dictate different protein interactions and complex formation explaining the different localization and role in the neuronal compartment, and the lower expression and stability of a-SMN.

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“…Five intragenic mutations were identified in six patients. All of the patients had been reported elsewhere [ 19 , 20 , 22 , 27 , 28 , 29 , 30 ], and clinical information on each patient is summarized in Table 1 . Mutations of Patients 1, 2, 4, 5, and 6 were analyzed in our laboratory.…”

Section: Methodsmentioning

confidence: 99%

“…All mutations are missense mutations except for T274YfsX32, which is a frame-shift mutation. These mutations were previously described elsewhere [19,20,22,[27][28][29][30]. To confirm the successful adjustment of the transfection efficiency of the plasmids containing SMN cDNA, HeLa cells were simultaneously transfected with a reference plasmid carrying the red fluorescence expression protein mCherry.…”

Section: Plasmid Construct Carrying Exogenous Smn Cdnamentioning

confidence: 99%

Stability and Oligomerization of Mutated SMN Protein Determine Clinical Severity of Spinal Muscular Atrophy

Niba

Nishio

Wijaya

et al. 2022

Genes

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Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disease characterized by defects of lower motor neurons. Approximately 95% of SMA patients are homozygous for survival motor neuron 1 (SMN1) gene deletion, while ~5% carry an intragenic SMN1 mutation. Here, we investigated the stability and oligomerization ability of mutated SMN1 proteins. Plasmids containing wild- and mutant-type SMN1 cDNA were constructed and transfected into HeLa cells. Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated similar abundances of transcripts from the plasmids containing SMN cDNA, but Western blotting showed different expression levels of mutated SMN1 proteins, reflecting the degree of their instability. A mutated SMN1 protein with T274YfsX32 exhibited a much lower expression level than other mutated SMN1 proteins with E134K, Y276H, or Y277C. In immunoprecipitation analysis, the mutated SMN1 protein with T274YfsX32 did not bind to endogenous SMN1 protein in HeLa cells, suggesting that this mutation completely blocks the oligomerization with full-length SMN2 protein in the patient. The patient with T274YfsX32 showed a much more severe phenotype than the other patients with different mutations. In conclusion, the stability and oligomerization ability of mutated SMN1 protein may determine the protein stability and may be associated with the clinical severity of SMA caused by intragenic SMN1 mutation.

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Two Japanese Patients With SMA Type 1 Suggest that Axonal-SMN May Not Modify the Disease Severity

Cited by 5 publications

References 12 publications

Phenotypes of SMA patients retaining SMN1 with intragenic mutation

Phenotypes of SMA patients retaining SMN1 with intragenic mutation

Different Stability and Proteasome-Mediated Degradation Rate of SMN Protein Isoforms

Stability and Oligomerization of Mutated SMN Protein Determine Clinical Severity of Spinal Muscular Atrophy

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