American Journal of Medical Genetics Neuropsychiatric Genetics) 114:354±359 2002) Sequencing of the GRIK1 Gene in Patients With Juvenile Absence Epilepsy Does Not Reveal Mutations Affecting Receptor Structure Claudia Izzi, 1 Alessandro Barbon, 1 Rebekka Kretz, 2 Thomas Sander, 2 and Sergio Barlati 1 * 1 Division of Biology and Genetics, Department of Biomedical Sciences and Biotechnologies, Brescia University Medical School, Brescia, Italy 2 Department of Neurology, University Hospital ChariteÂ, Campus Virchow Clinic, Humboldt University of Berlin, Berlin, Germany Hereditary factors play a major role in the etiology of juvenile absence epilepsy JAE) that is a common subtype of idiopathic generalized epilepsy IGE). Sander et al. [1997: Am J Med Genet 74:416±421] reported an allelic association of JAE with the nine- copy allele of a tetranucleotide repeat poly- morphism in the third intron of the kainate- selective GluR5 receptor gene GRIK1) and supportive evidence for linkage of IGE to GRIK1 in families of JAE probands. These ®ndings suggest that a major genetic deter- minant of GRIK1 confers susceptibility to JAE. Assuming that the GRIK1 tetranucleo- tiderepeatpolymorphismisunlikelytohave functional relevance itself, we have sequ- enced the coding regions and regulatory sequences of the GRIK1 gene in eight JAE patients who carry the nine-repeat allele of the GRIK1 tetranucleotide repeat polymor- phism to detect a putative functional GRIK1 mutation that is in linkage disequilibrium with the nine-repeat allele. Seven of them were derived from families showing positive evidence for linkage to GRIK1. Our muta- tion analysis of coding regions and splice junctions revealed only two silent poly- morphisms A522C and C1173T) out of the ®veSNPspresentinpublicdatabasesandno mutations affecting protein structure. No signi®cant differences were found in the allele frequencies of the detected poly- morphisms between the JAE patients and controls. High levels of sequence conserva- tion were also found in the promoter, in the 5 0 and both the 3 0 untranslated regions and in the RNA secondary structure involved in the editing reaction. The results presented indicate that mutations in the coding sequ- ences, in the intron-exon boundaries and in the main regulatory regions of the GRIK1 are not commonly involved in the etiology of JAE. ß 2002 Wiley-Liss, Inc. KEY WORDS: sequencing analysis; gluta- mate receptor; juvenile ab- sence epilepsy INTRODUCTION Epilepsy comprises a group of disorders that are characterized by recurrent unprovoked seizures caus- ing a transitory impairment of brain function due to a paroxysmal excessive cortical excitability and aberrant synchronization [Noebels, 1996]. Hereditary factors play a predominant role in the etiology of idiopathic generalized epilepsy IGE) that is characterized by recurring generalized seizures in the absence of detectable brain lesions or metabolic abnormalities [Beck-Mannagetta and Janz, 1991; Sander, 1996; Berkovic et al., 1998]. Recent molecular genetic studies revealed causative mutations in several genes encoding ion channels in three rare autosomal-dominant human idiopathic epilepsy syndromes [Hirose et al., 2000; Steinlein and Noebels, 2000]: voltage-sensitive potas- sium channel gene defects KCNQ2, KCNQ3) in benign familial neonatal convulsions, nicotinic acetylcholine receptor gene mutations CHRNA4, CHRNB2) in fami- lial nocturnal frontal lobe epilepsy [De Fusco, et al., 2000], and mutations in voltage-sensitive sodium channels SCN1B, SCN1A) and the g 2 subunit of the GABA A receptor in ``generalized epilepsy with febrile Grant sponsor: Consorzio Interuniversitario Biotecnologie CIB); Grant sponsor: MURST Centro Eccellenza IDET; Grant sponsor: German Research Community; Grant number: DFG Sa 434/2-2. *Correspondence to: Prof. Sergio Barlati, Division of Biology and Genetics, Department of Biomedical Sciences and Biotechnol- ogies, Brescia University Medical School, via Valsabbina 19, 25123 Brescia, Italy. E-mail: barlati@med.unibs.it Received 19 July 2001; Accepted 21 November 2001 DOI 10.1002/ajmg.10254 ß 2002 Wiley-Liss, Inc.