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Published on: September 25, 2013
Loss-of-function mutations in Lysyl-tRNA synthetase cause various leukoencephalopathy phenotypes
Chong Sun1, Jie Song1, Yanjun Jiang1
1Department of Neurology (C.S., J.S., C.Z., J. Lu, J.X., S. Luo, J. Lin), Huashan Hospital, Fudan University, Shanghai, China; Baylor Genetic Laboratories (Y.J., Z.N., M.L.L., M.W., R.E.P., H.M., Y.Y.), Houston, TX; Department of Radiology (Y.L.), Huashan Hospital, Fudan University; Department of Pathology (Y.W., M.G.), Huashan Hospital, Fudan University, Shanghai, China; Department of Biochemistry and Molecular Pharmacology (M.L., K.D., Y.-M.H.), Thomas Jefferson University, Philadelphia, PA; Department of Human Genetics (S.N.O., A.A.), University of Michigan Medical School, Ann Arbor, MI; Department of Pediatrics and Department of Obstetrics and Gynecology (S.L.), University of Hawaii School of Medicine, Honolulu, HI; Department of Medical Oncology and Therapeutics Research (T.P.S.), Division of Clinical Cancer Genetics, City of Hope National Medical Center, Duarte, CA; Department of Molecular and Human Genetics (P.L.M., A.L.M., L.E., S.R.L., Z.N., M.L.L., J.A.R., M.W., R.E.P., H.M., J.A.R., Y.Y., V.W.Z.), Baylor College of Medicine, Houston, TX; and AmCare Genomics Lab (V.W.Z.), Guangzhou, China.
Objective:
To expand the clinical spectrum of lysyl-tRNA synthetase (KARS) gene-related diseases, which so far includes Charcot-Marie-Tooth disease, congenital visual impairment and microcephaly, and nonsyndromic hearing impairment.
Methods:
Whole-exome sequencing was performed on index patients from 4 unrelated families with leukoencephalopathy. Candidate pathogenic variants and their cosegregation were confirmed by Sanger sequencing. Effects of mutations on KARS protein function were examined by aminoacylation assays and yeast complementation assays.
Results:
Common clinical features of the patients in this study included impaired cognitive ability, seizure, hypotonia, ataxia, and abnormal brain imaging, suggesting that the CNS involvement is the main clinical presentation. Six previously unreported and 1 known KARS mutations were identified and cosegregated in these families. Two patients are compound heterozygous for missense mutations, 1 patient is homozygous for a missense mutation, and 1 patient harbored an insertion mutation and a missense mutation. Functional and structural analyses revealed that these mutations impair aminoacylation activity of lysyl-tRNA synthetase, indicating that defective KARS function is responsible for the phenotypes in these individuals.
Conclusions:
Our results demonstrate that patients with loss-of-function KARS mutations can manifest CNS disorders, thus broadening the phenotypic spectrum associated with KARS-related disease.
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