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Prader-Willi syndrome is a multisystemic genetic disorder that can be associated with epilepsy. There is insufficient information concerning the clinical and electroencephalographic characteristics of epilepsy and the long-term outcome of these patients. The aim of this study is to describe seizure types, electroencephalographic patterns and long-term seizure outcome in Prader-Willi syndrome patients suffering from epilepsy. We retrospectively studied 38 patients with Prader-Willi syndrome and seizures. Results of neuroimaging studies were obtained for 35 individuals. We subdivided these patients into two groups: group A, 24 patients, without brain lesions; and group B, 11 patients, with brain abnormalities. All patients were re-evaluated after a period of at least 10 years. Twenty-one patients (55.2 %) were affected by generalized epilepsy and 17 patients (44.8 %) presented focal epilepsy. The most common seizure type was generalized tonic-clonic seizure. The mean age at seizure onset was 4.5 years (ranged from 1 month to 14 years). In the follow-up period, seizure freedom was achieved in 32 patients (84.2 %). Seizure freedom was associated with electroencephalographic normalization, while the six children presenting drug-resistant epilepsy showed persistence of electroencephalographic abnormalities. Group B patients showed a higher prevalence of drug-resistant epilepsy. Patients with Prader-Willi syndrome were frequently affected by generalized seizures. Most of the patients had a favorable evolution, although, patients with brain abnormalities presented a worse outcome, suggesting that the presence of these lesions can influence the response to antiepileptic therapy.

Pontocerebellar hypoplasia (PCH) type 1 is characterized by the co-occurrence of spinal anterior horn involvement and hypoplasia of the cerebellum and pons. EXOSC3 has been recently defined as a major cause of PCH type 1. Three different phenotypes showing variable severity have been reported. We identified a homozygous mutation [c.395A > C/p.D132A] in EXOSC3 in four patients with muscle hypotonia, developmental delay, spinal anterior horn involvement, and prolonged survival, consistent with the "mild PCH1 phenotype". Interestingly, isolated cerebellar hypoplasia limited to the hemispheres or involving both hemispheres and vermis was the main neuroradiologic finding, whereas the pontine volume was in the normal range for age. These findings strongly suggest that analysis of the EXOSC3 gene should be recommended also in patients with spinal anterior horn involvement and isolated cerebellar hypoplasia.

Recent studies reported mutations in the gene encoding the proline-rich transmembrane protein 2 (PRRT2) to be causative for paroxysmal kinesigenic dyskinesia (PKD), PKD combined with infantile seizures (ICCA), and benign familial infantile seizures (BFIS). PRRT2 is a presynaptic protein which seems to play an important role in exocytosis and neurotransmitter release. PKD is the most common form of paroxysmal movement disorder characterized by recurrent brief involuntary hyperkinesias triggered by sudden movements. Here, we sequenced PRRT2 in 14 sporadic and 8 familial PKD and ICCA cases of Caucasian origin and identified three novel mutations (c.919C>T/p.Gln307, c.388delG/p.Ala130Profs 46, c.884G>A/p.Arg295Gln) predicting two truncated proteins and one probably damaging point mutation. A review of all published cases is also included. PRRT2 mutations occur more frequently in familial forms of PRRT2-related syndromes (80-100 %) than in sporadic cases (33-46 %) suggesting further heterogeneity in the latter. PRRT2 mutations were rarely described in other forms of paroxysmal dyskinesias deviating from classical PKD, as we report here in one ICCA family without kinesigenic triggers. Mutations are exclusively found in two exons of the PRRT2 gene at a high rate across all syndromes and with one major mutation (c.649dupC) in a mutational hotspot of nine cytosines, which is responsible for 57 % of all cases in all phenotypes. We therefore propose that genetic analysis rapidly performed in early stages of the disease is highly cost-effective and can help to avoid further unnecessary diagnostic and therapeutic interventions.