title: Complete loss of P/Q calcium channel activity caused by a CACNA1A missense mutation carried by patients with episodic ataxia type 2.
abstract: Familial hemiplegic migraine, episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 are allelic disorders of the CACNA1A gene (coding for the alpha(1A) subunit of P/Q calcium channels), usually associated with different types of mutations (missense, protein truncating, and expansion, respectively). However, the finding of expansion and missense mutations in patients with EA2 has blurred this genotype-phenotype correlation. We report the first functional analysis of a new missense mutation, associated with an EA2 phenotype-that is, T-->C transition of nt 4747 in exon 28, predicted to change a highly conserved phenylalanine residue to a serine at codon 1491, located in the putative transmembrane segment S6 of domain III. Patch-clamp recording in HEK 293 cells, coexpressing the mutagenized human alpha(1A-2) subunit, together with human beta(4) and alpha(2)delta subunits, showed that channel activity was completely abolished, although the mutated protein is expressed in the cell. These results indicate that a complete loss of P/Q channel function is the mechanism underlying EA2, whether due to truncating or to missense mutations.
authors.affiliation: Department of Biology, Tor Vergata University, Rome, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Guida
authors.forename: F
authors.initials: F
authors.lastname: Trettel
authors.forename: S
authors.initials: S
authors.lastname: Pagnutti
authors.forename: E
authors.initials: E
authors.lastname: Mantuano
authors.forename: A
authors.initials: A
authors.lastname: Tottene
authors.forename: L
authors.initials: L
authors.lastname: Veneziano
authors.forename: T
authors.initials: T
authors.lastname: Fellin
authors.forename: M
authors.initials: M
authors.lastname: Spadaro
authors.forename: K
authors.initials: K
authors.lastname: Stauderman
authors.forename: M
authors.initials: M
authors.lastname: Williams
authors.forename: S
authors.initials: S
authors.lastname: Volsen
authors.forename: R
authors.initials: R
authors.lastname: Ophoff
authors.forename: R
authors.initials: R
authors.lastname: Frants
authors.forename: C
authors.initials: C
authors.lastname: Jodice
authors.forename: M
authors.initials: M
authors.lastname: Frontali
authors.forename: D
authors.initials: D
authors.lastname: Pietrobon
mesh_terms: D000595:Amino Acid Sequence; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D020865:Calcium Channels, P-Type / Q000235:genetics; D020907:Calcium Channels, Q-Type / Q000235:genetics; D002460:Cell Line; D002524:Cerebellar Ataxia / Q000145:classification / Q000235:genetics*; D002874:Chromosome Mapping; D002888:Chromosomes, Human, Pair 19; D005260:Female; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D010375:Pedigree; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D014162:Transfection; D020864:Calcium Channels, N-Type
chemical_list: D015220:Calcium Channels; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D021122:Protein Subunits; C105656:CACNA1A protein, human; D020864:Calcium Channels, N-Type