SMN transcript levels in leukocytes of SMA patients determined by absolute real-time PCR.
Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by homozygous mutations of the SMN1 gene. Three forms of SMA are recognized (type I-III) on the basis of clinical severity. All patients have at least one or more (usually 2-4) copies of a highly homologous gene (SMN2), which produces insufficient levels of functional SMN protein, because of alternative splicing of exon 7. Recently, evidence has been provided that SMN2 expression can be enhanced by pharmacological treatment. However, no reliable biomarkers are available to test the molecular efficacy of the treatments. At present, the only potential biomarker is the dosage of SMN products in peripheral blood. However, the demonstration that SMN full-length (SMN-fl) transcript levels are reduced in leukocytes of patients compared with controls remains elusive (except for type I). We have developed a novel assay based on absolute real-time PCR, which allows the quantification of SMN1-fl/SMN2-fl transcripts. For the first time, we have shown that SMN-fl levels are reduced in leukocytes of type II-III patients compared with controls. We also found that transcript levels are related to clinical severity as in type III patients SMN2-fl levels are significantly higher compared with type II and directly correlated with functional ability in type II patients and with age of onset in type III patients. Moreover, in haploidentical siblings with discordant phenotype, the less severely affected individuals showed significantly higher transcript levels. Our study shows that SMN2-fl dosage in leukocytes can be considered a reliable biomarker and can provide the rationale for SMN dosage in clinical trials.
Tiziano
Francesco Danilo
FD
Institute of Medical Genetics, Catholic University, Largo Francesco Vito, 1, 00168 Rome, Italy. fdtiziano@rm.unicatt.it
Pinto
Anna Maria
AM
Fiori
Stefania
S
Lomastro
Rosa
R
Messina
Sonia
S
Bruno
Claudio
C
Pini
Antonella
A
Pane
Marika
M
D'Amico
Adele
A
Ghezzo
Alessandro
A
Bertini
Enrico
E
Mercuri
Eugenio
E
Neri
Giovanni
G
Brahe
Christina
C
D000328:Adult; D016022:Case-Control Studies; D002940:Circadian Rhythm / Q000235:genetics; D005260:Female; D018628:Gene Dosage / Q000235:genetics; D005786:Gene Expression Regulation; D006579:Heterozygote; D006801:Humans; D007962:Leukocytes / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009134:Muscular Atrophy, Spinal / Q000235:genetics* / Q000503:physiopathology; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods*; D055540:Survival of Motor Neuron 2 Protein / Q000235:genetics*; D013997:Time Factors; D055815:Young Adult
D012333:RNA, Messenger; D055540:Survival of Motor Neuron 2 Protein