Mutations and deletions in PCDH19 account for various familial or isolated epilepsies in females

Abstract

Mutations in PCDH19, encoding protocadherin 19 on chromosome X, cause familial epilepsy and mental retardation limited to females or Dravet-like syndrome. Heterozygous females are affected while hemizygous males are spared, this unusual mode of inheritance being probably due to a mechanism called cellular interference. To extend the mutational and clinical spectra associated with PCDH19, we screened 150 unrelated patients (113 females) with febrile and afebrile seizures for mutations or rearrangements in the gene. Fifteen novel point mutations were identified in 15 female patients (6 sporadic and 9 familial cases). In addition, qPCR revealed two whole gene deletions and one partial deletion in 3 sporadic female patients. Clinical features were highly variable but included almost constantly a high sensitivity to fever and clusters of brief seizures. Interestingly, cognitive functions were normal in several family members of 2 families: the familial condition in family 1 was suggestive of Generalized Epilepsy with Febrile Seizures Plus (GEFS+) whereas all three affected females had partial cryptogenic epilepsy. These results show that mutations in PCDH19 are a relatively frequent cause of epilepsy in females and should be considered even in absence of family history and/or mental retardation.

Figure 1

Identification of 2 families with PCDH19 mutations, in which the majority of patients had normal cognitive functions. A) Pedigrees of the families and segregation analysis of the PCDH19 mutations; m/+ and m: individuals heterozygous and hemizygous for the mutation; +/+ and +: individuals homozygous and hemizygous for the wild-type allele. Dots in the middle of the squares: unaffected mutation carrier. The arrows indicate the index cases. B) Sequence electrophoregrams of the mutations. Mutation nomenclature is based on the PCDH19 transcript reference EF676096. Nucleotides are numbered according to the cDNA with +1 corresponding to the A of the ATG translation initiation codon in the reference sequence.

Figure 2

Identification of 3 families with PCDH19 deletions. A) Pedigrees of the families and segregation analysis of the PCDH19 deletions; del/+: individuals heterozygous for the deletion; +/+ and +: individuals homozygous and hemizygous for the wild-type allele, respectively. Upper right black corner: Generalized seizures; Upper left black corner: Partial seizures; Lower right black corner: FS; Lower left black corner: intellectual disability; hatched symbols: patients with rolandic epilepsy. The arrows indicate the index cases. B) Results of copy number dosage for each exon of PCDH19 using real time-Q-PCR. WT1 is a control female; WT2 is a control male.

Figure 3

Characterization of the size and breakpoints of the PCDH19 deletions using high-density SNP arrays (Illumina). A) Log R profiles of the 3 patients with deletions. The X-axis indicates the position on the chromosome X and the Y-axis indicates the log R. The grey stripes represent the location of the PCDH19 gene. B) Schematic representation of the deletions indicated by double arrows. The size of the deleted regions (in Mb of Kb) is indicated in brackets.