Fig. 2

a, b Renal biopsy taken at time of presentation (11 months of age) showing moderate tubulointerstitial damage and numerous immature glomeruli (arrow) (a). Masson trichrome, ×100 (b) (silver, ×200). c Electron Micrograph of renal biopsy: A tubular epithelial cell showing mildly enlarged mitochondria with a fluffy granular matrix (arrow). d Assessment of oxidative enzyme histochemistry in a muscle biopsy revealed a mosaic pattern of cytochrome c oxidase (COX) activity. Presence of fibres with subsarcolemmal aggregates of mitochondria (arrow) and some type II fibres devoid of activity (asterisk) (×600). e The assessment of individual respiratory chain enzyme activities in muscle identified a combined OXPHOS deficiency in the patient (blue bars) compared to controls (red bars); mean enzyme activities shown for muscle controls (n = 25) are set at 100 %. The activities of complexes I and IV were both severely decreased with complex III activity decreased to a lesser extent, and evidence of complex II activity being spared. f Familial segregation of the identified compound heterozygous RMND1 variants, a paternally-inherited p.Asn238Ser variant and a maternally-inherited p.Gln189* variant