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Background Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are clinically distinct neurodevelopmental genetic disorders that map to 15q11-q13. The primary phenotypes are attributable to loss of expression of imprinted genes within this region which can arise by means of a number of mechanisms. The most sensitive single approach to diagnosing both PWS and AS is to study methylation patterns within 15q11-q13; however many techniques exist for this purpose. Given the diversity of techniques available, there is a need for consensus testing and reporting guidelines. Methods Testing and reporting guidelines have been drawn up and agreed in accordance with the procedures of the UK Clinical Molecular Genetics Society and the European Molecular Genetics Quality Network. Results A practical set of molecular genetic testing and reporting guidelines has been developed for these two disorders. In addition, advice is given on appropriate reporting policies, including advice on test sensitivity and recurrence risks. In considering test sensitivity, the possibility of differential diagnoses is discussed. Conclusion An agreed set of practice guidelines has been developed for the diagnostic molecular genetic testing of PWS and AS.

An 11 months old boy, developed liver failure after febrile status epilepticus while being treated with valproic acid for myoclonic epilepsy and recurrent partial and generalized seizures. The diagnosis of Alpers-Huttenlocher disease was considered. A muscle biopsy showed mitochondrial dysfunction. Mitochondrial DNA depletion was ruled out. Sequencing of the polymerase gamma gene ( POLG1 ) did not detect any mutations. Sequencing of the alpha-1 subunit gene of the voltage-gated neuronal sodium channel ( SCN1A ) revealed a novel, de novo amino acid change p.Val 1637 Glu. This case expands the spectrum of clinical presentations related to mutations in SCN1A . We warn that children with SCN1A mutations may be at risk for developing liver failure following status epilepticus, due to mitochondrial dysfunction.

Background Dravet syndrome is a severe infantile epileptic encephalopathy caused in approximately 80% of cases by mutations in the voltage gated sodium channel subunit gene SCN1A . The majority of these mutations are de novo. The parental origin of de novo mutations varies widely among genetic disorders and the aim of this study was to determine this for Dravet syndrome. Methods 91 patients with de novo SCN1A mutations and their parents were genotyped for single nucleotide polymorphisms (SNPs) in the region surrounding their mutation. Allele specific polymerase chain reaction (PCR) based on informative SNPs was used to separately amplify and sequence the paternal and maternal alleles to determine in which parental chromosome the mutation arose. Results The parental origin of SCN1A mutations was established in 44 patients for whom both parents were available and SNPs were informative. The mutations were of paternal origin in 33 cases and of maternal origin in the remaining 11 cases. De novo mutation of SCN1A most commonly, but not exclusively, originates from the paternal chromosome. The average age of parents originating mutations did not differ from that of the general population. Conclusions The greater frequency of paternally derived mutations in SCN1A is likely to be due to the greater chance of mutational events during the increased number of mitoses which occur during spermatogenesis compared to oogenesis, and the greater susceptibility to mutagenesis of the methylated DNA characteristic of sperm cells.