title: Unstable insertion in the 5' flanking region of the cystatin B gene is the most common mutation in progressive myoclonus epilepsy type 1, EPM1.
abstract: Progressive myoclonus epilepsy type 1 (EPM1, also known as Unverricht-Lundborg disease) is an autosomal recessive disorder characterized by progressively worsening myoclonic jerks, frequent generalized tonic-clonic seizures, and a slowly progressive decline in cognition. Recently, two mutations in the cystatin B gene (also known as stefin B, STFB) mapping to 21q22.3 have been implicated in the EPM1 phenotype: a G-->C substitution in the last nucleotide of intron 1 that was predicted to cause a splicing defect in one family, and a C-->T substitution that would change an Arg codon (CGA) to a stop codon (TGA) at amino acid position 68, resulting in a truncated cystatin B protein in two other families. A fourth family showed undetectable amounts of STFB mRNA by northern blot analysis in an affected individual. We present haplotype and mutational analyses of our collection of 20 unrelated EPM1 patients and families from different ethnic groups. We identify four different mutations, the most common of which consists of an unstable approximately 600-900 bp insertion which is resistant to PCR amplification. This insertion maps to a 12-bp polymorphic tandem repeat located in the 5' flanking region of the STFB gene, in the region of the promoter. The size of the insertion varies between different EPM1 chromosomes sharing a common haplotype and a common origin, suggesting some level of meiotic instability over the course of many generations. This dynamic mutation, which appears distinct from conventional trinucleotide repeat expansions, may arise via a novel mechanism related to the instability of tandemly repeated sequences.
authors.affiliation: Centre for Research in Neuroscience, McGill Univ., Montreal, Quebec, Canada. bhgr@musicb.mcgill.ca
authors.forename: R G
authors.initials: RG
authors.lastname: Lafrenière
authors.forename: D L
authors.initials: DL
authors.lastname: Rochefort
authors.forename: N
authors.initials: N
authors.lastname: Chrétien
authors.forename: J M
authors.initials: JM
authors.lastname: Rommens
authors.forename: J I
authors.initials: JI
authors.lastname: Cochius
authors.forename: R
authors.initials: R
authors.lastname: Kälviäinen
authors.forename: U
authors.initials: U
authors.lastname: Nousiainen
authors.forename: G
authors.initials: G
authors.lastname: Patry
authors.forename: K
authors.initials: K
authors.lastname: Farrell
authors.forename: B
authors.initials: B
authors.lastname: Söderfeldt
authors.forename: A
authors.initials: A
authors.lastname: Federico
authors.forename: B R
authors.initials: BR
authors.lastname: Hale
authors.forename: O H
authors.initials: OH
authors.lastname: Cossio
authors.forename: T
authors.initials: T
authors.lastname: Sørensen
authors.forename: M A
authors.initials: MA
authors.lastname: Pouliot
authors.forename: T
authors.initials: T
authors.lastname: Kmiec
authors.forename: P
authors.initials: P
authors.lastname: Uldall
authors.forename: J
authors.initials: J
authors.lastname: Janszky
authors.forename: M R
authors.initials: MR
authors.lastname: Pranzatelli
authors.forename: F
authors.initials: F
authors.lastname: Andermann
authors.forename: E
authors.initials: E
authors.lastname: Andermann
authors.forename: G A
authors.initials: GA
authors.lastname: Rouleau
mesh_terms: D001483:Base Sequence; D002891:Chromosomes, Human, Pair 21; D055313:Cystatin B; D015891:Cystatins / Q000235:genetics*; D015853:Cysteine Proteinase Inhibitors / Q000235:genetics; D017931:DNA Primers; D004251:DNA Transposable Elements; D004831:Epilepsies, Myoclonic / Q000235:genetics*; D005260:Female; D006239:Haplotypes; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D010375:Pedigree; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: C524994:CSTB protein, human; D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D017931:DNA Primers; D004251:DNA Transposable Elements; D055313:Cystatin B