Hypertrophic olivary degeneration on magnetic resonance imaging in mitochondrial syndromes associated with POLG and SURF1 mutations

Hypertrophic olivary degeneration (HOD) is associated with lesions within the dento-rubro-olivary pathway or Guillain-Mollaret triangle and may be associated clinically with palatal tremor. Here we report HOD on brain magnetic resonance (MR) imaging in three patients with progressive mitochondrial syndromes in the absence of palatal tremor. Two of the patients were found to have identical compound heterozygous mutations in the POLG gene, encoding the catalytic subunit of the mitochondrial DNA polymerase-γ, but presented with different clinical phenotypes. The first patient displayed the clinical syndrome of sensory ataxia, neuropathy, dysarthria, and ophthalmoparesis (SANDO), while the second patient was affected by a neurological disorder consisting of an ophthalmoplegia, myopathy, and neuropathy. The third case was a child with Leigh syndrome due to SURF1 gene mutations, who presented with a generalized tremor. We discuss the brain MR imaging findings in these three cases along with a literature review on the MR features of previously reported cases of patients with POLG gene mutations and Leigh disease due to SURF1 gene mutations. Our findings suggest that the presence of HOD, in the appropriate clinical setting, should alert the clinician to the possibility of a mitochondrial disorder and the need to screen for mutations in POLG and SURF1 genes.

Molecular mousetraps and the serpinopathies1

Members of the serine proteinase inhibitor or serpin superfamily inhibit their target proteinases by a remarkable conformational transition that involves the enzyme being translocated more than 70 Å (1 Å=10−10 m) from the upper to the lower pole of the inhibitor. This elegant mechanism is subverted by point mutations to form ordered polymers that are retained within the endoplasmic reticulum of secretory cells. The accumulation of polymers underlies the retention of mutants of α1-antitrypsin and neuroserpin within hepatocytes and neurons to cause cirrhosis and dementia respectively. The formation of polymers results in the failure to secrete mutants of other members of the serpin superfamily: antithrombin, C1 inhibitor and α1-antichymotrypsin, to cause a plasma deficiency that results in the clinical syndromes of thrombosis, angio-oedema and emphysema respectively. Understanding the common mechanism underlying the retention and deficiency of mutants of the serpins has allowed us to group these conditions as the serpinopathies. We review in this paper the molecular and structural basis of the serpinopathies and show how this has allowed the development of specific agents to block the polymerization that underlies disease.

Intraneuronal Aβ, non-amyloid aggregates and neurodegeneration in a Drosophila model of Alzheimer’s disease

We have developed models of Alzheimer's disease in Drosophila melanogaster by expressing the Abeta peptides that accumulate in human disease. Expression of wild-type and Arctic mutant (Glu22Gly) Abeta(1-42) peptides in Drosophila neural tissue results in intracellular Abeta accumulation followed by non-amyloid aggregates that resemble diffuse plaques. These histological changes are associated with progressive locomotor deficits and vacuolation of the brain and premature death of the flies. The severity of the neurodegeneration is proportional to the propensity of the expressed Abeta peptide to form oligomers. The fly phenotype is rescued by treatment with Congo Red that reduces Abeta aggregation in vitro. Our model demonstrates that intracellular accumulation and non-amyloid aggregates of Abeta are sufficient to cause the neurodegeneration of Alzheimer's disease. Moreover it provides a platform to dissect the pathways of neurodegeneration in Alzheimer's disease and to develop novel therapeutic interventions.