Jonatan Halvardson

Hadassah Medical Center, Yerushalayim, Jerusalem District, Israel

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Publications (7)49.29 Total impact

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    ABSTRACT: Isolated metabolic myopathies encompass a heterogeneous group of disorders, with mitochondrial myopathies being a subgroup, with depleted skeletal muscle energy production manifesting either by recurrent episodes of myoglobinuria or progressive muscle weakness. In this study, we investigated the genetic cause of a patient from a consanguineous family who presented with adolescent onset autosomal recessive mitochondrial myopathy. Analysis of enzyme activities of the five respiratory chain complexes in our patients' skeletal muscle showed severely impaired activities of iron sulfur (Fe-S)-dependent complexes I, II and III and mitochondrial aconitase. We employed exome sequencing combined with homozygosity mapping to identify a homozygous mutation, c.1A>T, in the FDX1L gene, which encodes the mitochondrial ferredoxin 2 (Fdx2) protein. The mutation disrupts the ATG initiation translation site resulting in severe reduction of Fdx2 content in the patient muscle and fibroblasts mitochondria. Fdx2 is the second component of the Fe-S cluster biogenesis machinery, the first being IscU that is associated with isolated mitochondrial myopathy. We suggest adding genetic analysis of FDX1L in cases of mitochondrial myopathy especially when associated with reduced activity of the respiratory chain complexes I, II and III.European Journal of Human Genetics advance online publication, 27 November 2013; doi:10.1038/ejhg.2013.269.
    European journal of human genetics: EJHG 11/2013; · 3.56 Impact Factor
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    ABSTRACT: The starting material for RNA sequencing (RNA-seq) studies is usually total RNA or polyA+RNA. Both forms of RNA represent heterogeneous pools of RNA molecules at different levels of maturation and processing. Such heterogeneity, in addition to the biases associated with polyA+purification steps, may influence the analysis, sensitivity and the interpretation of RNA-seq data. We hypothesize that subcellular fractions of RNA may provide a more accurate picture of gene expression. We present results for sequencing of cytoplasmic and nuclear RNA after cellular fractionation of tissue samples. In comparison with conventional polyA+RNA, the cytoplasmic RNA contains a significantly higher fraction of exonic sequence, providing increased sensitivity in expression analysis and splice junction detection, and in improved de novo assembly of RNA-seq data. Conversely, the nuclear fraction shows an enrichment of unprocessed RNA compared with total RNA-seq, making it suitable for analysis of nascent transcripts and RNA processing dynamics. Our results show that cellular fractionation is a more rapid and cost effective approach than conventional polyA+enrichment when studying mature RNAs. Thus, RNA-seq of separated cytosolic and nuclear RNA can significantly improve the analysis of complex transcriptomes from mammalian tissues.
    BMC Biotechnology 11/2013; 13(1):99. · 2.17 Impact Factor
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    ABSTRACT: Linkage, association and expression studies previously pointed to the human QKI, KH domain containing, RNA-binding (QKI) as a candidate gene for schizophrenia. Functional studies of the mouse ortholog Qk focused mainly on its role in oligodendrocyte development and myelination, while its function in astroglia remained unexplored. Here we show that QKI is highly expressed in human primary astrocytes and that its splice forms encode proteins targeting different sub-cellular localizations. Uncovering the role of QKI in astrocytes is of interest in light of growing evidence implicating astrocyte dysfunction in the pathogenesis of several disorders of the central nervous system. We selectively silenced QKI splice variants in human primary astrocytes and used RNA sequencing to identify differential expression and splice variant composition at the genome-wide level. We found that mRNA expression of Glial fibrillary acidic protein (GFAP), encoding a major component of astrocyte intermediate filaments, was down-regulated after QKI7 splice variant silencing. Moreover, we identified a potential QKI binding site within the 3'untranslated region of human GFAP. This sequence was not conserved between mice and humans, raising the possibility that GFAP is a target for QKI in humans but not rodents. Haloperidol treatment of primary astrocytes resulted in coordinated increases in QKI7 and GFAP expression. Taken together, our results provide the first link between QKI and GFAP, two genes with alterations previously observed independently in schizophrenic patients. Our findings for QKI, together with its well-known role in myelination, suggest that QKI is a hub regulator of glia function in humans.
    Human Molecular Genetics 01/2013; · 7.69 Impact Factor
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    Jonatan Halvardson, Ammar Zaghlool, Lars Feuk
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    ABSTRACT: RNA sequencing has become an important method to perform hypothesis-free characterization of global gene expression. One of the limitations of RNA sequencing is that most sequence reads represent highly expressed transcripts, whereas low level transcripts are challenging to detect. To combine the benefits of traditional expression arrays with the advantages of RNA sequencing, we have used whole exome enrichment prior to sequencing of total RNA. We show that whole exome capture can be successfully applied to cDNA to study the transcriptional landscape in human tissues. By introducing the exome enrichment step, we are able to identify transcripts present at very low levels, which are below the level of detection in conventional RNA sequencing. Although the enrichment increases the ability to detect presence of transcripts, it also lowers the accuracy of quantification of expression levels. Our results yield a large number of novel exons and splice isoforms, suggesting that conventional RNA sequencing methods only detect a small fraction of the full transcript diversity. We propose that whole exome enrichment of RNA is a suitable strategy for genome-wide discovery of novel transcripts, alternative splice variants and fusion genes.
    Nucleic Acids Research 08/2012; · 8.81 Impact Factor
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    ABSTRACT: The molecular etiology of primary intractable epilepsy in infancy is largely unknown. We studied a nonconsanguineous Moroccan-Jewish family, where three of their seven children presented with intractable seizures and died at 18-36 months. Homozygous regions were searched using 250 K DNA single nucleotide polymorphism (SNP) array. The sequence of 50 Mb exome of a single patient was determined using SOLiD 5500XL deep sequencing analyzer. A single homozygous 11.3 Mb genomic region on chromosome 6 was linked to the disease in this family. This region contained 110 genes encoding a total of 1,000 exons. Whole exome sequencing revealed a single pathogenic homozygous variant within the critical region. The mutation, Phe229Leu in the EFHC1 gene was previously shown, in a carrier state, to be associated with juvenile myoclonic epilepsy. Although heterozygosity for the Phe229Leu mutation is known to be associated with a relatively benign form of epilepsy in adolescence; homozygosity for the same mutation is associated with lethal epilepsy of infancy. Given the considerable carrier rate of this mutation worldwide, the sequence of the EFHC1 gene should be determined in all patients with primary intractable epilepsy in infancy.
    Epilepsia 06/2012; 53(8):1436-40. · 3.96 Impact Factor
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    ABSTRACT: Degeneration of the cerebrum, cerebellum, and retina in infancy is part of the clinical spectrum of lysosomal storage disorders, mitochondrial respiratory chain defects, carbohydrate glycosylation defects, and infantile neuroaxonal dystrophy. We studied eight individuals from two unrelated families who presented at 2-6 months of age with truncal hypotonia and athetosis, seizure disorder, and ophthalmologic abnormalities. Their course was characterized by failure to acquire developmental milestones and culminated in profound psychomotor retardation and progressive visual loss, including optic nerve and retinal atrophy. Despite their debilitating state, the disease was compatible with survival of up to 18 years. Laboratory investigations were normal, but the oxidation of glutamate by muscle mitochondria was slightly reduced. Serial brain MRI displayed progressive, prominent cerebellar atrophy accompanied by thinning of the corpus callosum, dysmyelination, and frontal and temporal cortical atrophy. Homozygosity mapping followed by whole-exome sequencing disclosed a Ser112Arg mutation in ACO2, encoding mitochondrial aconitase, a component of the Krebs cycle. Specific aconitase activity in the individuals' lymphoblasts was severely reduced. Under restrictive conditions, the mutant human ACO2 failed to complement a yeast ACO1 deletion strain, whereas the wild-type human ACO2 succeeded, indicating that this mutation is pathogenic. Thus, a defect in mitochondrial aconitase is associated with an infantile neurodegenerative disorder affecting mainly the cerebellum and retina. In the absence of noninvasive biomarkers, determination of the ACO2 sequence or of aconitase activity in lymphoblasts are warranted in similarly affected individuals, based on clinical and neuroradiologic grounds.
    The American Journal of Human Genetics 03/2012; 90(3):518-23. · 11.20 Impact Factor
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    ABSTRACT: Transcriptome sequencing allows for analysis of mature RNAs at base pair resolution. Here we show that RNA-seq can also be used for studying nascent RNAs undergoing transcription. We sequenced total RNA from human brain and liver and found a large fraction of reads (up to 40%) within introns. Intronic RNAs were abundant in brain tissue, particularly for genes involved in axonal growth and synaptic transmission. Moreover, we detected significant differences in intronic RNA levels between fetal and adult brains. We show that the pattern of intronic sequence read coverage is explained by nascent transcription in combination with co-transcriptional splicing. Further analysis of co-transcriptional splicing indicates a correlation between slowly removed introns and alternative splicing. Our data show that sequencing of total RNA provides unique insight into the transcriptional processes in the cell, with particular importance for normal brain development.
    Nature Structural & Molecular Biology 11/2011; 18(12):1435-40. · 11.90 Impact Factor

Publication Stats

72 Citations
49.29 Total Impact Points

Institutions

  • 2012
    • Hadassah Medical Center
      Yerushalayim, Jerusalem District, Israel
    • Ha'Emek Medical Center
      Naẕerat, Northern District, Israel
  • 2011–2012
    • Uppsala University
      • The Rudbeck Laboratory
      Uppsala, Uppsala, Sweden