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KARS1 encodes a lysyl-transfer RNA synthetase (LysRS) that links lysine to its cognate tRNA. Two different KARS1 isoforms exert functional effects in cytosol and mitochondria. Bi-allelic pathogenic variants in KARS1 have been associated to sensorineural hearing and visual loss, neuropathy, seizures, and leukodystrophy. We report the clinical, biochemical and neuroradiological features of nine individuals with KARS1-related disorder carrying 12 different variants with nine of them being novel. The consequences of these variants on the cytosol and/or mitochondrial LysRS were functionally validated in yeast mutants. Most cases presented with severe neurological features including congenital and progressive microcephaly, seizures, developmental delay/intellectual disability, and cerebral atrophy. Oculo-motor dysfunction and immuno-hematological problems were present in six and three cases, respectively. A yeast growth defect of variable severity was detected for most variants on both cytosolic and mitochondrial isoforms. The detrimental effects of two variants on yeast growth were partially rescued by lysine supplementation. Congenital progressive microcephaly, oculo-motor dysfunction and immuno-hematological problems are emerging phenotypes in KARS1-related disorders. The data in yeast emphasize the role of both mitochondrial and cytosolic isoforms in the pathogenesis of KARS1-related disorder and supports the therapeutic potential of lysine supplementation at least in a subset of patients. This article is protected by copyright. All rights reserved.

Background Elevated serum ferritin levels are common findings in clinical practice, usually caused by inflammation, liver disease, high alcohol consumption or malignancy, although it can occur in association with rare genetic conditions. Case presentation We describe a male in his sixties with persistent hyperferritinaemia without associated iron overload and subsequent development of cataract. The patient himself suggested hyperferritinaemia-cataract syndrome as a diagnosis, which was subsequently confirmed with mutation analysis of the light chain ferritin (FTL) gene. Such mutations are inherited in an autosomal dominant pattern. Interpretation Mutations in FTL are known to interfere with the balance between iron levels and ferritin production. When common causes of hyperferritinaemia are excluded, rare conditions should be considered in order to avoid unnecessary procedures and treatment. Genetic analyses are available for all clinicians and should be requested upon the right indications.