Microdeletions involving the SCN1A gene may be common in SCN1A-mutation-negative SMEI patients.
Severe myoclonic epilepsy of infancy (SMEI) or Dravet syndrome is a rare epilepsy syndrome. In 30 to 70% of SMEI patients, truncating and missense mutations in the neuronal voltage-gated sodium-channel alpha-subunit gene (SCN1A) have been identified. The majority of patients have truncating mutations that are predicted to be loss-of-function alleles. Because mutation detection studies use PCR-based sequencing or conformation sensitive gel electrophoresis (CSGE), microdeletions, which are also predicted to be loss-of-function alleles, can easily escape detection. We selected 11 SMEI patients with or without additional features who had no SCN1A mutation detectable with sequencing analysis. In addition, none of the patients was heterozygous for any of the SNPs in SCN1A, indicating that they were either homozygous for all SNPs or hemizygous due to a microdeletion of the gene. We subsequently analyzed these patients for the presence of microdeletions in SCN1A using a quantitative PCR method named multiplex amplicon quantification (MAQ), and observed three patients missing one copy of the SCN1A gene. All three microdeletions were confirmed by fluorescence in situ hybridization (FISH). These findings demonstrate that a substantial percentage of SCN1A-mutation-negative SMEI patients with or without additional features carry a chromosomal microdeletion comprising the SCN1A gene and that haploinsufficiency of the SCN1A gene is a cause of SMEI.
Suls
Arvid
A
Neurogenetics Group, Department of Molecular Genetics, Flanders Interuniversity Institute for Biotechnology (VIB), University of Antwerp, Antwerp, Belgium.
Claeys
Kristl G
KG
Goossens
Dirk
D
Harding
Boris
B
Van Luijk
Rob
R
Scheers
Stefaan
S
Deprez
Liesbet
L
Audenaert
Dominique
D
Van Dyck
Tine
T
Beeckmans
Sabine
S
Smouts
Iris
I
Ceulemans
Berten
B
Lagae
Lieven
L
Buyse
Gunnar
G
Barisic
Nina
N
Misson
Jean-Paul
JP
Wauters
Jan
J
Del-Favero
Jurgen
J
De Jonghe
Peter
P
Claes
Lieve R F
LR
D002648:Child; D002874:Chromosome Mapping; D018389:Codon, Nonsense; D004252:DNA Mutational Analysis; D004831:Epilepsies, Myoclonic / Q000175:diagnosis / Q000235:genetics*; D005260:Female; D017353:Gene Deletion; D005820:Genetic Testing / Q000379:methods; D006239:Haplotypes; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007223:Infant; D008297:Male; D020125:Mutation, Missense; D062550:NAV1.1 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D015222:Sodium Channels / Q000235:genetics*
D018389:Codon, Nonsense; D062550:NAV1.1 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; C568242:SCN1A protein, human; D015222:Sodium Channels