RT Journal Article SR Electronic T1 Severe phenotypic spectrum of biallelic mutations in PRRT2 gene JF Journal of Neurology, Neurosurgery & Psychiatry JO J Neurol Neurosurg Psychiatry FD BMJ Publishing Group Ltd SP 782 OP 785 DO 10.1136/jnnp-2014-309025 VO 86 IS 7 A1 Marion Delcourt A1 Florence Riant A1 Josette Mancini A1 Mathieu Milh A1 Vincent Navarro A1 Emmanuel Roze A1 Véronique Humbertclaude A1 Christian Korff A1 Vincent Des Portes A1 Pierre Szepetowski A1 Diane Doummar A1 Bernard Echenne A1 Samuel Quintin A1 Nicolas Leboucq A1 Rabbind Singh Amrathlal A1 Jacques Rochette A1 Agathe Roubertie YR 2015 UL http://jnnp.bmj.com/content/86/7/782.abstract AB Background Heterozygous dominant mutations of PRRT2 have been associated with various types of paroxysmal neurological manifestations, including benign familial infantile convulsions and paroxysmal kinesigenic dyskinesia. The phenotype associated with biallelic mutations is not well understood as few cases have been reported.Methods PRRT2 screening was performed by Sanger sequencing and quantitative multiplex PCR of short fluorescent fragments. A CGH array was used to characterise the size of the deletion at the 16p11.2 locus.Results Five patients with homozygous or compound heterozygous deleterious PRRT2 gene mutations are described. These patients differ from those with a single mutation by their overall increased severity: (1) the combination of at least three different forms of paroxysmal neurological disorders within the same patient and persistence of paroxysmal attacks; (2) the occurrence of uncommon prolonged episodes of ataxia; and (3) the association of permanent neurological disorders including learning difficulties in four patients and cerebellar atrophy in 2.Conclusions Our observations expand the phenotype related to PRRT2 insufficiency, and highlight the complexity of the phenotype associated with biallelic mutations, which represents a severe neurological disease with various paroxysmal disorders and frequent developmental disabilities.