Mutation in the COX4I1 gene is associated with short stature, poor weight gain and increased chromosomal breaks, simulating Fanconi anemia

Abstract

We describe a novel autosomal recessive form of mitochondrial disease in a child with short stature, poor weight gain, and mild dysmorphic features with highly suspected Fanconi anemia due to a mutation in COX4I1 gene. Whole Exome Sequencing was performed then followed by Sanger confirmation, identified a K101N mutation in COX4I1, segregating with the disease. This nuclear gene encodes the common isoform of cytochrome c oxidase (COX) subunit 4 (COX 4-1), an integral regulatory part of COX (respiratory chain complex IV) the terminal electron acceptor of the mitochondrial respiratory chain. The patient's fibroblasts disclosed decreased COX activity, impaired ATP production, elevated ROS production, decreased expression of COX4I1 mRNA and undetectable (COX4) protein. COX activity and ATP production were restored by lentiviral transfection with the wild-type gene. Our results demonstrate the first human mutation in the COX4I1 gene linked to diseases and confirm its role in the pathogenesis. Thus COX4I1 mutations should be considered in any patient with features suggestive of this diagnosis.

Figure 1

Patient features. The figure shows photographs of the patients’ facial (a) and hand (b) features at the age of 5 years (with parental permission).

Figure 2

Evolutionary conservation of Lys-101 in the COX4I1 gene. The mutated conserved residue is highlighted.

Figure 3

COX enzymatic activity and ATP production in patient’s fibroblasts. Fibroblast from controls n=3, patient (Pt), patient cells transformed with a control lenti-virus (Pt+CV) and patient cells transformed with a lenti virus containing the wild-type COX 4I1 (Pt+ COX 4I1) were assayed for COX enzymatic activity (a), expressed as COX normalized to citrate synthase activity (U COX/U CS) and for ATP production (b), expressed as relative luminescence (RLU) normalized to cell content (A620). *P<0.05.

Figure 4

Western blot analysis. Twenty micrograms protein per slot obtained from mitochondria, isolated from patient (Pt) and controls (n=3) fibroblasts were subjected to Urea-SDS-PAGE and Western blot with antibodies against complexes I (CI), II (CII) and subunits 1, 2 and 4 of complex IV (COX) and visualized by ECL (A). The graph depicts intensities normalized to CII.