Three patients born to the same set of consanguineous parents presented with antenatal skin oedema, hypotonia, cardiomyopathy and tubulopathy. The enzymatic activities of multiple mitochondrial respiratory chain complexes were reduced in muscle. Marked reduction of 12s rRNA, the core of the mitochondrial small ribosomal subunit, was found in fibroblasts. Homozygosity mapping led to the identification of a mutation in the MRPS22 gene, which encodes a mitochondrial ribosomal protein. Transfection of the patient cells with wild‐type MRPS22 cDNA increased the 12s rRNA content and normalised the enzymatic activities. Quantification of mitochondrial transcripts is advisable in patients with multiple defects of the mitochondrial respiratory chain.
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