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Am J Med Genet A. 2015 Oct;167A(10):2314-8. doi: 10.1002/ajmg.a.37152. Epub 2015 May 10.

Variable clinical expression in patients with mosaicism for KCNQ2 mutations.

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Inserm, UMR_S 910, Génétique Médicale et Génomique Fonctionnelle, Marseille, France.
Aix Marseille Université, GMGF, Faculté de Médecine, Marseille, France.
APHM, Hôpital d'Enfants de La Timone, Service de Neurologie Pédiatrique, Marseille, France.
APHM, Hôpital d'Enfants de La Timone, Département de Génétique Médicale, Marseille, France.
Département de Biochimie et Génétique, CHU d'Angers, Angers, France.
APHP, Hôpital Trousseau, Service de génétique clinique et Service de neuropédiatrie, Paris, France.
Clinique de Génétique, Hôpital Jeanne de Flandre, Lille, France.
Centre Hospitalier des Pays de Morlaix, Pédiatrie et Néonatalogie, Morlaix, France.
Département de Génétique Médicale, Hospices Civils de Lyon, Université Lyon 1, Lyon, France.


Mutations in the KCNQ2 gene, encoding a potassium channel subunit, were reported in patients presenting epileptic phenotypes of varying severity. Patients affected by benign familial neonatal epilepsy (BFNE) are at the milder end of the spectrum, they are affected by early onset epilepsy but their subsequent neurological development is usually normal. Mutations causing BFNE are often inherited from affected parents. Early infantile epileptic encephalopathy type 7 (EIEE7) is at the other end of the severity spectrum and, although EIEE7 patients have early onset epilepsy too, their neurological development is impaired and they will present motor and intellectual deficiency. EIEE7 mutations occur de novo. Electrophysiological experiments suggested a correlation between the type of mutation and the severity of the disease but intra and interfamilial heterogeneity exist. Here, we describe the identification of KCNQ2 mutation carriers who had children affected with a severe epileptic phenotype, and found that these individuals were mosaic for the KCNQ2 mutation. These findings have important consequences for genetic counseling and indicate that neurological development can be normal in the presence of somatic mosaicism for a KCNQ2 mutation.


BFNE; EIEE7; KCNQ2; encephalopathy; epilepsy; genetic counseling; somatic mosaicism

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