Fatal infantile mitochondrial encephalomyopathy, hypertrophic cardiomyopathy and optic atrophy associated with a homozygous OPA1 mutation

BACKGROUND

Infantile-onset encephalopathy and hypertrophic cardiomyopathy caused by mitochondrial oxidative phosphorylation defects are genetically heterogeneous with defects involving both the mitochondrial and nuclear genomes.

OBJECTIVE

To identify the causative genetic defect in two sisters presenting with lethal infantile encephalopathy, hypertrophic cardiomyopathy and optic atrophy.

METHODS

We describe a comprehensive clinical, biochemical and molecular genetic investigation of two affected siblings from a consanguineous family. Molecular genetic analysis was done by a combined approach involving genome-wide autozygosity mapping and next-generation exome sequencing. Biochemical analysis was done by enzymatic analysis and Western blot. Evidence for mitochondrial DNA (mtDNA) instability was investigated using long-range and real-time PCR assays. Mitochondrial cristae morphology was assessed with transmission electron microscopy.

RESULTS

Both affected sisters presented with a similar cluster of neurodevelopmental deficits marked by failure to thrive, generalised neuromuscular weakness and optic atrophy. The disease progression was ultimately fatal with severe encephalopathy and hypertrophic cardiomyopathy. Mitochondrial respiratory chain complex activities were globally decreased in skeletal muscle biopsies. They were found to be homozygous for a novel c.1601T>G (p.Leu534Arg) mutation in the OPA1 gene, which resulted in a marked loss of steady-state levels of the native OPA1 protein. We observed severe mtDNA depletion in DNA extracted from the patients' muscle biopsies. Mitochondrial morphology was consistent with abnormal mitochondrial membrane fusion.

CONCLUSIONS

We have established, for the first time, a causal link between a pathogenic homozygous OPA1 mutation and human disease. The fatal multisystemic manifestations observed further extend the complex phenotype associated with pathogenic OPA1 mutations, in particular the previously unreported association with hypertrophic cardiomyopathy. Our findings further emphasise the vital role played by OPA1 in mitochondrial biogenesis and mtDNA maintenance.

Posttraumatic active bleeding of mediastinal mixed vascular malformation: a case report

A case of an actively bleeding mediastinal mass in a 4-year-old boy who sustained multitrauma is described. A computed tomography (CT) scan of the chest upon admission demonstrated a mediastinal mass, which enlarged significantly as seen by repeat CT scan at 3 days with a concomitant drop in serum hemoglobin levels. The lesion was excised, and pathological examination established the diagnosis of a lymphatic-venous malformation containing bloody fluid. Lymphatic-venous malformations are rare vascular malformations and are usually found in the head and neck and less commonly at other sites. Spontaneous bleeding is a known complication, and there are few reports describing posttraumatic hemorrhage. Our case is the first description in the English medical literature of a posttraumatic bleeding mediastinal mixed vascular malformation and includes sequential CT scans illustrating the dynamic nature of hemorrhage.