KARS-related diseases: Progressive leukoencephalopathy with brainstem and spinal cord calcifications as new phenotype and a review of literature

Background: KARS encodes lysyl-transfer ribonucleic acid (tRNA) synthetase, which catalyzes the aminoacylation of tRNA-Lys in the cytoplasm and mitochondria. Eleven families/sporadic patients and 16 different mutations in KARS have been reported to date. The associated clinical phenotype is heterogeneous ranging from early onset encephalopathy to isolated peripheral neuropathy or nonsyndromic hearing impairment. Recently additional presentations including leukoencephalopathy as predominant cerebral involvement or cardiomyopathy, isolated or associated with muscular and cerebral involvement, have been reported. A progressive Leukoencephalopathy with brainstem and spinal cord calcifications was previously described in a singleton patient and in two siblings, without the identification of the genetic cause. We reported here about a new severe phenotype associated with biallelic KARS mutations and sharing some common points with the other already reported phenotypes, but with a distinct clinical and neuroimaging picture. Review of KARS mutant patients published to date will be also discussed. Results: Herein, we report the clinical, biochemical and molecular findings of 2 unreported Italian patients affected by developmental delay, acquired microcephaly, spastic tetraparesis, epilepsy, sensory-neural hypoacusia, visual impairment, microcytic hypochromic anaemia and signs of hepatic dysfunction. MRI pattern in our patients was characterized by progressive diffuse leukoencephalopathy and calcifications extending in cerebral, brainstem and cerebellar white matter, with spinal cord involvement. Genetic analysis performed on these 2 patients and in one subject previously described with similar MRI pattern revealed the presence of biallelic mutations in KARS in all 3 subjects. Conclusions: With our report we define the molecular basis of the previously described Leukoencephalopathy with Brainstem and Spinal cord Calcification widening the spectrum of KARS related disorders, particularly in childhood onset disease suggestive for mitochondrial impairment. The review of previous cases does not suggest a strict and univocal genotype/phenotype correlation for this highly heterogeneous entity. Moreover, our cases confirm the usefulness of search for common brain and spine MR imaging pattern and of broad genetic screening, in syndromes clinically resembling mitochondrial disorders in spite of normal biochemical assay

Loss of the sphingolipid desaturase DEGS1 causes hypomyelinating leukodystrophy.

Sphingolipid imbalance is the culprit in a variety of neurological diseases, some affecting the myelin sheath. We have used whole-exome sequencing in patients with undetermined leukoencephalopathies to uncover the endoplasmic reticulum lipid desaturase DEGS1 as the causative gene in 19 patients from 13 unrelated families. Shared features among the cases include severe motor arrest, early nystagmus, dystonia, spasticity, and profound failure to thrive. MRI showed hypomyelination, thinning of the corpus callosum, and progressive thalamic and cerebellar atrophy, suggesting a critical role of DEGS1 in myelin development and maintenance. This enzyme converts dihydroceramide (DhCer) into ceramide (Cer) in the final step of the de novo biosynthesis pathway. We detected a marked increase of the substrate DhCer and DhCer/Cer ratios in patients' fibroblasts and muscle. Further, we used a knockdown approach for disease modeling in Danio rerio, followed by a preclinical test with the first-line treatment for multiple sclerosis, fingolimod (FTY720, Gilenya). The enzymatic inhibition of Cer synthase by fingolimod, 1 step prior to DEGS1 in the pathway, reduced the critical DhCer/Cer imbalance and the severe locomotor disability, increasing the number of myelinating oligodendrocytes in a zebrafish model. These proof-of-concept results pave the way to clinical translation

Genome sequencing in persistently unsolved white matter disorders

Genetic white matter disorders have heterogeneous etiologies and overlapping clinical presentations. We performed a study of the diagnostic efficacy of genome sequencing in 41 unsolved cases with prior exome sequencing, resolving an additional 14 from an historical cohort (n = 191). Reanalysis in the context of novel disease-associated genes and improved variant curation and annotation resolved 64% of cases. The remaining diagnoses were directly attributable to genome sequencing, including cases with small and large copy number variants (CNVs) and variants in deep intronic and technically difficult regions. Genome sequencing, in combination with other methodologies, achieved a diagnostic yield of 85% in this retrospective cohort.Guy Helman, Bryan R. Lajoie, Joanna Crawford, Asako Takanohashi, Marzena Walkiewicz ... Stephen J. Bent ... et al

RMND1-related leukoencephalopathy with temporal lobe cysts and hearing loss—another mendelian mimicker of congenital cytomegalovirus infection

Background Leukoencephalopathy with temporal lobe cysts may be associated with monogenetic conditions such as Aicardi–Goutières syndrome or RNASET2 mutations and with congenital infections such as cytomegalovirus. In view of the fact that congenital cytomegalovirus is difficult to confirm outside the neonatal period, excluding a Mendelian disorder is extremely relevant, changing family planning and medical management in affected families. We performed diagnostic testing in individuals with leukoencephalopathy with temporal lobe cysts without a definitive diagnosis of congenital cytomegalovirus infection. Methods We reviewed a large-scale biorepository of patients with unsolved leukodystrophies and identified two individuals with required for meiotic nuclear division 1 (RMND1) mutations and similar magnetic resonance imaging (MRI) features, including temporal lobe cysts. Ten additional subjects with confirmed RMND1 mutations were identified as part of a separate disease specific cohort. Brain MRIs from all 12 individuals were reviewed for common neuroradiological features. Results MRI features in RMND1 mutations included temporal lobe swelling, with rarefaction and cystic evolution, enlarged tips of the temporal lobes, and multifocal subcortical white matter changes with confluent periatrial T2 signal hyperintensity. A combination of these features was present in ten of the 12 individuals reviewed. Conclusions Despite the small number of reported individuals with RMND1 mutations, a clinically recognizable phenotype of leukoencephalopathy with temporal lobe swelling, rarefaction, and cystic changes has emerged in a subset of individuals. Careful clinical phenotyping, including for lactic acidosis, deafness, and severe muscle involvement seen in RMND1 mutation positive individuals, and MRI pattern recognition will be important in differentiating these patients from children with congenital infections like cytomegalovirus

Severe dystonia, cerebellar atrophy, and cardiomyopathy likely caused by a missense mutation in TOR1AIP1.

BackgroundDystonia, cerebellar atrophy, and cardiomyopathy constitute a rare association.MethodsWe used homozygosity mapping and whole exome sequencing to determine the mutation, western blot and immunolabelling on cultured fibroblasts to demonstrate the lower expression and the mislocalization of the protein.ResultsWe report on a boy born from consanguineous healthy parents, who presented at three years of age with rapidly progressing dystonia, progressive cerebellar atrophy, and dilated cardiomyopathy. We identified regions of homozygosity and performed whole exome sequencing that revealed a homozygous missense mutation in TOR1AIP1. The mutation, absent in controls, results in a change of a highly conserved glutamic acid to alanine. TOR1AIP1 encodes lamina-associated polypeptide 1 (LAP1), a transmembrane protein ubiquitously expressed in the inner nuclear membrane. LAP1 interacts with torsinA, the protein mutated in DYT1-dystonia. In vitro studies in fibroblasts of the patient revealed reduced expression of LAP1 and its mislocalization and aggregation in the endoplasmic reticulum as underlying pathogenic mechanisms.Conclusions and relevanceThe pathogenic role of TOR1AIP1 mutation is supported by a) the involvement of a highly conserved amino acid, b) the absence of the mutation in controls, c) the functional interaction of LAP1 with torsinA, and d) mislocalization of LAP1 in patient cells. Of note, cardiomyopathy has been reported in LAP1-null mice and in patients with the TOR1AIP1 nonsense mutation. Other cases will help delineate the clinical spectrum of LAP1-related mutations

Role of Decreased Levels of Fis Histone-Like Protein in Crohn's Disease-Associated Adherent Invasive Escherichia coli LF82 Bacteria Interacting with Intestinal Epithelial Cells▿

The interaction of Crohn's disease (CD)-associated adherent-invasive Escherichia coli (AIEC) strain LF82 with intestinal epithelial cells depends on surface appendages, such as type 1 pili and flagella. Histone-like proteins operate as global regulators to control the expression of these virulence factors. We evaluated the role of histone-like proteins in AIEC reference strain LF82 during infection of intestinal epithelial cells, Intestine-407, and observed that the fis mRNA level was decreased. The role of Fis in AIEC LF82 was determined by studying the phenotype of an LF82 fis::Km mutant. This was the first mutant of strain LF82 that has been described thus far that is unable to express flagellin but still able to produce type 1 pili. The cyclic-di-GMP pathway linking flagella and type 1 pilus expression is not involved in Fis-mediated regulation, and we identified in the present study Fis-binding sites located upstream of the fimE gene and in the intergenic region between fimB and nanC of the fim operon encoding type 1 pili. The major consequence of decreased Fis expression in AIEC bacteria in contact with host cells is a direct downregulation of fimE expression, leading to the preferential ON phase of the fimS element. Thus, by maintaining type 1 pilus expression, AIEC bacteria, which interact with the gut mucosa, have greater ability to colonize and to induce inflammation in CD patients

Mutation in the AGK gene in two siblings with unusual Sengers syndrome

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