Quantification of SMN protein in leucocytes from spinal muscular atrophy patients: effects of treatment with valproic acid.
BACKGROUND
Spinal muscular atrophy (SMA) is caused by the homozygous deletion of the survival motor neuron (SMN)1 gene. The nearly identical SMN2 gene produces small amounts of full-length mRNA and functional SMN protein, due to a point mutation in a critical splicing site. Increasing SMN protein production by histone deacetylase inhibiting drugs such as valproic acid (VPA) is an experimental treatment strategy for SMA.


OBJECTIVE
To investigate whether an SMN-specific ELISA could detect changes in SMN protein expression in peripheral blood mononuclear cells (PBMCs) after treatment with VPA.


METHODS
The authors developed a sensitive SMN-specific ELISA. Six patients with SMA types 2 and 3 participated in the study. Recombinant SMN calibration curves were used to calculate SMN protein levels in PBMCs before and after 4&emsp14;months of VPA treatment.


RESULTS
The SMN ELISA was able to detect small differences in SMN protein concentrations, and differences in SMN protein levels in Epstein-Barr virus immortalised lymphocyte cell lines from SMA type 1 and 2 patients, carriers and healthy individuals (p<0.05). The mean SMN protein level in PBMCs from SMA patients was 22% (SD 15%) of the value in a healthy control. VPA treatment resulted in significantly increased SMN protein levels in five out of six SMA patients compared with baseline values (p<0.05), but did not restore SMN levels to normal values.


CONCLUSIONS
SMN protein quantification by this SMN ELISA is a useful additional tool for evaluating the effects of experimental treatment in SMA.
Piepers
Sanne
S
Rudolf Magnus Institute of Neuroscience, Department of Neurology, University Medical Centre Utrecht, The Netherlands. s.piepers-2@umcutrecht.nl
Cobben
Jan-Maarten
JM
Sodaar
Peter
P
Jansen
Marc D
MD
Wadman
Renske I
RI
Meester-Delver
Ann
A
Poll-The
Bwee Tien
BT
Lemmink
Henny H
HH
Wokke
John H J
JH
van der Pol
W-Ludo
WL
van den Berg
Leonard H
LH
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D018682:GABA Agents / Q000494:pharmacology*; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000378:metabolism; D008297:Male; D014897:Spinal Muscular Atrophies of Childhood / Q000188:drug therapy* / Q000378:metabolism*; D055533:Survival of Motor Neuron 1 Protein / Q000378:metabolism*; D016896:Treatment Outcome; D014635:Valproic Acid / Q000494:pharmacology*
D018682:GABA Agents; D055533:Survival of Motor Neuron 1 Protein; D014635:Valproic Acid