KCNQ2 and KCNQ3—potassium channel genes which are mutated in benign familial neonatal convulsions (BFNC) and other epilepsies
Generalized idiopathic epilepsies (IGE) cause 40% of all seizures and commonly have a genetic basis. One type of IGE is Benign Familial Neonatal Convulsions (BFNC), a dominantly inherited disorder of newborns. A submicroscopic deletion of chromosome 20q13.3 which co-segregates with seizures in a BFNC family has been identified. Characterization of cDNAs spanning the deleted region identified a novel voltage-gated potassium channel, KCNQ2, which belongs to a new KCNQ1-like class of potassium channels. Nine other BFNC probands were shown to have KCNQ2 mutations including three missense mutations, three frameshifts, two nonsense mutations, and one splice site mutation. A second gene, KCNQ3, was found in a separate BFNC family in which the mutation had been localized to chromosome 8. A missense mutation was found in this gene in perfect cosegregation with the BFNC phenotype in this latter family. This demonstrates that defects in potassium channels can cause epilepsy. Furthermore, some members of one of the BFNC families with a mutation in KCNQ2 also exhibited rolandic epilepsy and one individual with juvenile myoclonic epilepsy has a mutation in an alternative exon of KCNQ3.
1. A method for diagnosing the presence of a mutation in human KCNQ2 which causes BFNC or rolandic epilepsy wherein said method is performed by means which identify the presence of said mutation, and wherein said mutation is the presence of a G at nucleotide number 978 of SEQ ID NO:1, an A at nucleotide number 1043 of SEQ ID NO:1, a T at nucleotide number 1094 of SEQ ID NO:1, an A at nucleotide number 1125 of SEQ ID NO:1, a T at nucleotide 1469 of SEQ ID NO:1, an insertion of two nucleotides between nucleotides 975 and 976 of SEQ ID NO:1, an insertion of 5 nucleotides after nucleotide 2736 of SEQ ID NO:1, a deletion of 13 nucleotides consisting of nucleotides 1691–1703 of SEQ ID NO:1, an A rather than a G at the 3′ end of the intron which interrupts codon 544 of SEQ ID NO:2, a mutation resulting in a stop codon at or before codon 319 of SEQ ID NO:2, a mutation resulting in a stop codon at or before codon 524 of SEQ ID NO:2, a mutation resulting in a stop codon at or before codon 323 of SEQ ID NO:2, or a mutation resulting in a stop codon at or before codon 448 of SEQ ID NO:2.
2. The method of claim 1 wherein said means comprises sequencing human KCNQ2.
3. A method for diagnosing a mutation which causes BFNC or rolandic epilepsy comprising sequencing KCNQ2 in a patient's sample of DNA to determine the presence or absence of mutations which cause BFNC or rolandic epilepsy, wherein said said mutation is the presence of a G at nucleotide number 978 of SEQ ID NO:1, an A at nucleotide number 1043 of SEQ ID NO:1, a T at nucleotide 1094 of SEQ ID NO:1, an A at nucleotide 1125, a T at nucleotide 1469 of SEQ ID NO:1, an insertion of two nucleotides between nucleotides 975 and 976 of SEQ ID NO:1, an insertion of 5 nucleotides after nucleotide 2736 of SEQ ID NO:1, a deletion of 13 nucleotides consisting of nucleotides 1691–1703 of SEQ ID NO:1, or an A rather than a G at the 3′ end of the intron which interrupts codon 544 of SEQ ID NO:2.
4. The method of claim 3 wherein said patient's sample of DNA has been amplified.
5. A method for diagnosing a mutation which causes BFNC or rolandic epilepsy wherein said method comprises sequencing a KCNQ2 gene in a patient's sample of RNA to determine the presence or absence of mutations which cause BFNC or rolandic epilepsy, wherein said said mutation is the presence of a G at nucleotide number 978 of SEQ ID NO:1, an A at nucleotide number 1043 of SEQ ID NO:1, a T at nucleotide 1094 of SEQ ID NO:1, an A at nucleotide 1125, a T at nucleotide 1469 of SEQ ID NO:1, an insertion of two nucleotides between nucleotides 975 and 976 of SEQ ID NO:1, an insertion of 5 nucleotides after nucleotide 2736 of SEQ ID NO:1, a deletion of 13 nucleotides consisting of nucleotides 1691–1703 of SEQ ID NO:1, or an A rather than a G at the 3′ end of the intron which interrupts codon 544 of SEQ ID NO:2.
6. A method for diagnosing a mutation which causes BFNC or rolandic epilepsy wherein said method comprises determining KCNQ2 sequence in a patient by preparing cDNA from RNA taken from said patient and sequencing said cDNA to determine the presence or absence of mutations which cause BFNC or rolandic epilepsy, wherein said said mutation is the presence of a G at nucleotide number 978 of SEQ ID NO:1, an A at nucleotide number 1043 of SEQ ID NO:1, a T at nucleotide 1094 of SEQ ID NO:1, an A at nucleotide 1125, a T at nucleotide 1469 of SEQ ID NO:1, an insertion of two nucleotides between nucleotides 975 and 976 of SEQ ID NO:1, an insertion of 5 nucleotides after nucleotide 2736 of SEQ ID NO:1, a deletion of 13 nucleotides consisting of nucleotides 1691–1703 of SEQ ID NO:1, or an A rather than a G at the 3′ end of the intron which interrupts codon 544 of SEQ ID NO:2.
7. A pair of single-stranded DNA primers for determination of a nucleotide sequence of KCNQ2by a polymerase chain reaction, wherein the use of said primers in a polymerase chain reaction results in the synthesis of DNA having all or part of the sequence of KCNQ2, wherein KCNQ2 comprises the nucleotide sequence set forth in SEQ ID NO:1 and wherein said pair is selected from:
SEQ ID NO:27 and SEQ ID NO:28.
8. An isolated fragment of the DNA of SEQ ID NO: 1, wherein said fragment consists of at least 15 consecutive nucleotides of bases 1315–3232 of SEQ ID NO:1.
9. An isolated fragment of the DNA of SEQ ID NO: 1, wherein said fragment consists of at least 8 consecutive nucleotides of bases 1315–3232 of SEQ ID NO:1.