Kaja Kristine Selmer

SLC9A6 Mutations Cause X-Linked Mental Retardation, Microcephaly, Epilepsy, and Ataxia, a Phenotype Mimicking Angelman Syndrome

Linkage analysis and DNA sequencing in a family exhibiting an X-linked mental retardation (XLMR) syndrome, characterized by microcephaly, epilepsy, ataxia, and absent speech and resembling Angelman syndrome, identified a deletion in the SLC9A6 gene encoding the Na(+)/H(+) exchanger NHE6. Subsequently, other mutations were found in a male with mental retardation (MR) who had been investigated for Angelman syndrome and in two XLMR families with epilepsy and ataxia, including the family designated as having Christianson syndrome. Therefore, mutations in SLC9A6 cause X-linked mental retardation. Additionally, males with findings suggestive of unexplained Angelman syndrome should be considered as potential candidates for SLC9A6 mutations.

Spastic paraplegia type 7 is associated with multiple mitochondrial DNA deletions

Spastic paraplegia 7 is an autosomal recessive disorder caused by mutations in the gene encoding paraplegin, a protein located at the inner mitochondrial membrane and involved in the processing of other mitochondrial proteins. The mechanism whereby paraplegin mutations cause disease is unknown. We studied two female and two male adult patients from two Norwegian families with a combination of progressive external ophthalmoplegia and spastic paraplegia. Sequencing of SPG7 revealed a novel missense mutation, c.2102A>C, p.H 701P, which was homozygous in one family and compound heterozygous in trans with a known pathogenic mutation c.1454_1462del in the other. Muscle was examined from an additional, unrelated adult female patient with a similar phenotype caused by a homozygous c.1047insC mutation in SPG7. Immunohistochemical studies in skeletal muscle showed mosaic deficiency predominantly affecting respiratory complex I, but also complexes III and IV. Molecular studies in single, microdissected fibres showed multiple mitochondrial DNA deletions segregating at high levels (38–97%) in respiratory deficient fibres. Our findings demonstrate for the first time that paraplegin mutations cause accumulation of mitochondrial DNA damage and multiple respiratory chain deficiencies. While paraplegin is not known to be directly associated with the mitochondrial nucleoid, it is known to process other mitochondrial proteins and it is possible therefore that paraplegin mutations lead to mitochondrial DNA deletions by impairing proteins involved in the homeostasis of the mitochondrial genome. These studies increase our understanding of the molecular pathogenesis of SPG7 mutations and suggest that SPG7 testing should be included in the diagnostic workup of autosomal recessive, progressive external ophthalmoplegia, especially if spasticity is present.

CHD2 mutations in Lennox-Gastaut syndrome.

Lennox-Gastaut syndrome (LGS) is an epileptic encephalopathy with a heterogeneous etiology. In this study, we aimed to explore the role of CHD2 in LGS, as CHD2 mutations have been described recently in various epileptic encephalopathies. We have previously identified one patient with a large deletion affecting the CHD2 gene in a group of 22 patients with LGS or LGS-like epilepsy. In the remaining 17 patients without known etiology, Sanger sequencing revealed a de novo 1-bp duplication in the CHD2 gene in another patient. This mutation leads to a frameshift and, consequently, a premature stop codon 49bp downstream of the mutation. The patient had prominent myoclonic seizures and photosensitivity, thus, sharing phenotypic features with previously reported patients with CHD2-related epilepsy. In our original material of 22 patients with LGS features, we have now found two (9%) with mutations in the CHD2 gene. Our findings suggest that CHD2 mutations are important in the etiological spectrum of LGS.

Good outcome in patients with early dietary treatment of GLUT‐1 deficiency syndrome: results from a retrospective Norwegian study

The aim of this study was to characterize patients diagnosed with glucose transporter protein‐1 deficiency syndrome (GLUT‐1 DS) clinically and genetically, and to evaluate the effect of treatment with the classic ketogenic or modified Atkins diet.

FILTUS: a desktop GUI for fast and efficient detection of disease-causing variants, including a novel autozygosity detector

Summary: FILTUS is a stand-alone tool for working with annotated variant files, e.g. when searching for variants causing Mendelian disease. Very flexible in terms of input file formats, FILTUS offers efficient filtering and a range of downstream utilities, including statistical analysis of gene sharing patterns, detection of de novo mutations in trios, quality control plots and autozygosity mapping. The autozygosity mapping is based on a hidden Markov model and enables accurate detection of autozygous regions directly from exome-scale variant files. Availability and implementation: FILTUS is written in Python and runs on Windows, Mac and Linux. Binaries and source code are freely available at http://folk.uio.no/magnusv/filtus.html and on GitHub: https://github.com/magnusdv/filtus. Automatic installation is available via PyPI (e.g. pip install filtus). Contact: magnusdv@medisin.uio.no Supplementary information: Supplementary data are available at Bioinformatics online.

Parental SCN1A mutation mosaicism in familial Dravet syndrome

Different SCN1A mutations are known to cause a variety of phenotypes, such as generalized epilepsy with febrile seizures plus (GEFS+), Dravet syndrome and familial hemiplegic migraine (FHM). In Dravet syndrome, most mutations are de novo and familial cases are rare. In this study, Dravet syndrome is observed in two maternal half sisters. They have healthy fathers and their common mother has never experienced seizures, but has a lifelong history of migraine. Direct sequencing of DNA extracted from blood revealed a heterozygous SCN1A nonsense mutation c.3985C>T in the sisters, but not in the mother. The mutation induces a premature stop codon and probably leads to a non‐functional protein. Further examination of the mothers DNA showed that she has a mosaicism of the mutation. This report of parental SCN1A nonsense mutation mosaicism in familial Dravet syndrome suggests that mosaicism might be more common than previously suspected and emphasizes the importance of taking mosaicism into account in genetic counselling of Dravet syndrome and SCN1A mutations. Furthermore, whether the migraine of the mother could be influenced by her SCN1A mutation mosaicism is not known, but increased awareness of migraine in future studies of SCN1A related epilepsies could clarify this intriguing link between migraine and epilepsy.

Does ketogenic diet improve cognitive function in patients with GLUT1-DS? A 6- to 17-month follow-up study

The aim of this study was to investigate the effects of ketogenic diet (KD) on cognitive function in patients with glucose transporter protein 1 deficiency syndrome (GLUT1-DS). Six patients with GLUT1-DS who were referred to the National Centre for Epilepsy in Norway during the period of November 2011-September 2013 were included. They were diagnosed with GLUT1-DS on the basis of early-onset seizures and developmental delay (with or without movement disorders or microcephaly) in addition to CSF-to-blood glucose ratio below 0.5. They were all treated with either classical KD or modified Atkins diet (MAD). The effect of the diet with >90% reduction in the seizure frequency was, in retrospect, considered as a support for the diagnosis. The patients underwent standardized neuropsychological assessment before the diet was initiated, and they were reassessed after a minimum of six months on the diet. The neuropsychological tests were individually selected for each patient in order to match their cognitive level. The main finding was a considerable improvement in several aspects of neuropsychological functioning after 6-17 months of dietary treatment in all the six patients. The greatest progress was seen in the youngest children. Our findings suggest that early diagnosis and dietary treatment are important in order to prevent developmental delay. However, also adults with GLUT1-DS may profit from dietary treatment by improving alertness, setting the stage for enhanced learning capacity, as well as physical endurance and quality of life.

Copy number variants in adult patients with Lennox–Gastaut syndrome features

PURPOSE Lennox-Gastaut syndrome (LGS) is a severe epileptic encephalopathy with complex etiology. To explore possible genetic predispositions and causes of LGS, we have searched for copy number variants (CNVs). METHODS We studied 21 patients with LGS or LGS-like epilepsy for CNVs using whole-genome array comparative genomic hybridization (aCGH). KEY FINDINGS Eight patients (38%) carried rare CNVs that might contribute to their phenotype. The pathogenicity could be questioned in some of them, but in four patients (19%) a causative role was considered highly probable. Three had CNVs and clinical features consistent with known genetic syndromes: 22q13.3 deletion, 2q23.1 deletion, and MECP2 duplication. SIGNIFICANCE There is a high frequency of rare CNVs in adult patients with LGS-like epilepsy. The phenotypes of these background disorders may be obscured by the effects of intractable seizures and massive antiepileptic drug treatment. Previously, syndromic disorders were primarily identified by their clinical features; however, a genome wide approach with identification of the genotype might shed light on the phenotype.

SCN1A mutation screening in adult patients with Lennox–Gastaut syndrome features

Mutations in the SCN1A gene have been identified in a variety of epilepsy phenotypes, from severe encephalopathies such as Dravet syndrome to milder familial forms such as generalized epilepsy with febrile seizures plus. In a previous study, an SCN1A mutation was also identified in a patient with Lennox-Gastaut syndrome (LGS), and the aim of our study was to investigate the importance of mutations in the SCN1A gene in Norwegian patients with clinical features of LGS. We screened 22 adult patients for SCN1A mutations by direct sequencing of DNA and for micro-rearrangements with multiplex ligation-dependent probe amplification. In one patient a mutation was found, which demonstrates a clinical overlap between LGS and Dravet syndrome. This finding emphasizes the significance of SCN1A mutations also in epileptic disorders with features of LGS, particularly in the myoclonic variant of the disorder.

A mild form of Mucopolysaccharidosis IIIB diagnosed with targeted next-generation sequencing of linked genomic regions

Next-generation sequencing (NGS) techniques have already shown their potential in the identification of mutations underlying rare inherited disorders. We report here the application of linkage analysis in combination with targeted DNA capture and NGS to a Norwegian family affected by an undiagnosed mental retardation disorder with an autosomal recessive inheritance pattern. Linkage analysis identified two loci on chromosomes 9 and 17 which were subject to target enrichment by hybridization to a custom microarray. NGS achieved 20-fold or greater sequence coverage of 83% of all protein-coding exons in the target regions. This led to the identification of compound heterozygous mutations in NAGLU, compatible with the diagnosis of Mucopolysaccharidosis IIIB (MPS IIIB or Sanfilippo Syndrome type B). This diagnosis was confirmed by demonstrating elevated levels of heparan sulphate in urine and low activity of α-N-acetyl-glucosaminidase in cultured fibroblasts. Our findings describe a mild form of MPS IIIB and illustrate the diagnostic potential of targeted NGS in Mendelian disease with unknown aetiology.