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Treatment of spinal muscular atrophy cells with drugs that upregulate SMN expression reveals inter- and intra-patient variability.

ABSTRACT: Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder caused by mutations in the SMN1 gene. The homologous copy (SMN2) is always present in SMA patients. SMN1 gene transcripts are usually full-length (FL), but exon 7 is spliced out in a high proportion of SMN2 transcripts (delta7) (?7). Advances in drug therapy for SMA have shown that an increase in SMN mRNA and protein levels can be achieved in vitro. We performed a systematic analysis of SMN expression in primary fibroblasts and EBV-transformed lymphoblasts from seven SMA patients with varying clinical severity and different SMN1 genotypes to determine expression differences in two accessible tissues (skin and blood). The basal expression of SMN mRNA FL and ?7 in fibroblasts and lymphoblasts was analyzed by quantitative real-time PCR. The FL-SMN and FL/?7 SMN ratios were higher in control cells than in patients. Furthermore, we investigated the response of these cell lines to hydroxyurea, valproate and phenylbutyrate, drugs previously reported to upregulate SMN2. The response to treatments with these compounds was heterogeneous. We found both intra-patient and inter-patient variability even within haploidentical siblings, suggesting that tissue and individual factors may affect the response to these compounds. To optimize the stratification of patients in clinical trials, in vitro studies should be performed before enrolment so as to define each patient as a responder or non-responder to the compound under investigation.

SUBMITTER: Also-Rallo E

PROVIDER: S-EPMC3190259 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature

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Treatment of spinal muscular atrophy cells with drugs that upregulate SMN expression reveals inter- and intra-patient variability.

Also-Rallo Eva E Alías Laura L Martínez-Hernández Rebeca R Caselles Lidia L Barceló María J MJ Baiget Montserrat M Bernal Sara S Tizzano Eduardo F EF

European journal of human genetics : EJHG 20110525 10

Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder caused by mutations in the SMN1 gene. The homologous copy (SMN2) is always present in SMA patients. SMN1 gene transcripts are usually full-length (FL), but exon 7 is spliced out in a high proportion of SMN2 transcripts (delta7) (Δ7). Advances in drug therapy for SMA have shown that an increase in SMN mRNA and protein levels can be achieved in vitro. We performed a systematic analysis of SMN expression in primary fibroblasts and EB ...[more]

PMID: 21610752

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Project description:Clinical severity and treatment response vary significantly between patients with spinal muscular atrophy. The approval of therapies and the emergence of neonatal screening programmes urgently require a more detailed understanding of the genetic variants that underlie this clinical heterogeneity. We systematically investigated genetic variation other than SMN2 copy number in the SMN locus. Data were collected through our single-centre, population-based study on spinal muscular atrophy in the Netherlands, including 286 children and adults with spinal muscular atrophy Types 1-4, including 56 patients from 25 families with multiple siblings with spinal muscular atrophy. We combined multiplex ligation-dependent probe amplification, Sanger sequencing, multiplexed targeted resequencing and digital droplet polymerase chain reaction to determine sequence and expression variation in the SMN locus. SMN1, SMN2 and NAIP gene copy number were determined by multiplex ligation-dependent probe amplification. SMN2 gene variant analysis was performed using Sanger sequencing and RNA expression analysis of SMN by droplet digital polymerase chain reaction. We identified SMN1-SMN2 hybrid genes in 10% of spinal muscular atrophy patients, including partial gene deletions, duplications or conversions within SMN1 and SMN2 genes. This indicates that SMN2 copies can vary structurally between patients, implicating an important novel level of genetic variability in spinal muscular atrophy. Sequence analysis revealed six exonic and four intronic SMN2 variants, which were associated with disease severity in individual cases. There are no indications that NAIP1 gene copy number or sequence variants add value in addition to SMN2 copies in predicting the clinical phenotype in individual patients with spinal muscular atrophy. Importantly, 95% of spinal muscular atrophy siblings in our study had equal SMN2 copy numbers and structural changes (e.g. hybrid genes), but 60% presented with a different spinal muscular atrophy type, indicating the likely presence of further inter- and intragenic variabilities inside as well as outside the SMN locus. SMN2 gene copies can be structurally different, resulting in inter- and intra-individual differences in the composition of SMN1 and SMN2 gene copies. This adds another layer of complexity to the genetics that underlie spinal muscular atrophy and should be considered in current genetic diagnosis and counselling practices.

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Treatment of spinal muscular atrophy cells with drugs that upregulate SMN expression reveals inter- and intra-patient variability.

Publications

Treatment of spinal muscular atrophy cells with drugs that upregulate SMN expression reveals inter- and intra-patient variability.

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