Homozygous deletion in MICU1 presenting with fatigue and lethargy in childhood
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Updated: Mar 22, 2026
In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila
Published on: August 20, 2019
David Lewis-Smith1, Kimberli J Kamer1, Helen Griffin1
1Wellcome Trust Centre for Mitochondrial Research (D.L.-S., H.G., J.D., A.P., R.W.T., P.Y.-W.-M., R.H., P.F.C.), Institute of Genetic Medicine (D.L.-S., H.G., J.D., A.P., P.Y.-W.-M., R.H.), and Institute of Neuroscience (R.W.T.), Newcastle University, Newcastle upon Tyne, United Kingdom; Howard Hughes Medical Institute (K.J.K., D.T., V.K.M.), Department of Molecular Biology, Massachusetts General Hospital, Boston, MA; Department of Paediatric Neurology (A.-M.C., K.P.), The General Infirmary, Leeds, United Kingdom; Department of Child Neurology (V.R.), The Royal Victoria Infirmary, Newcastle upon Tyne Hospitals NHS Trust, Newcastle upon Tyne, United Kingdom; Department of Systems Biology (V.K.M.), Harvard Medical School, Boston, MA; Broad Institute (V.K.M.), Cambridge, MA; Department of Clinical Neurosciences (P.F.C.), University of Cambridge; and MRC Mitochondrial Biology Unit (P.F.C.), Cambridge Biomedical Campus, United Kingdom.
Objective:
To define the mechanism responsible for fatigue, lethargy, and weakness in 2 cousins who had a normal muscle biopsy.
Methods:
Exome sequencing, long-range PCR, and Sanger sequencing to identify the pathogenic mutation. Functional analysis in the patient fibroblasts included oxygen consumption measurements, extracellular acidification studies, Western blotting, and calcium imaging, followed by overexpression of the wild-type protein.
Results:
Analysis of the exome sequencing depth revealed a homozygous deletion of exon 1 of MICU1 within a 2,755-base pair deletion. No MICU1 protein was detected in patient fibroblasts, which had impaired mitochondrial calcium uptake that was rescued through the overexpression of the wild-type allele.
Conclusions:
MICU1 mutations cause fatigue and lethargy in patients with normal mitochondrial enzyme activities in muscle. The fluctuating clinical course is likely mediated through the mitochondrial calcium uniporter, which is regulated by MICU1.
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