Infantile and childhood onset PLA2G6-associated neurodegeneration in a large North African cohort.

BACKGROUND AND PURPOSE: Mutations in the PLA2G6 gene are causative of PLA2G6-associated neurodegeneration (PLAN), a spectrum of neurodegenerative conditions including infantile, childhood and adult onset forms. METHODS: Seventeen North African patients with a clinical suspicion of infantile-onset PLAN underwent clinical, neurophysiological and neuroimaging examinations, and PLA2G6 sequencing. Haplotype analysis was performed to date the identified founder mutation. RESULTS: All patients carried biallelic mutations in PLA2G6. Sixteen children had the commonest form of infantile-onset PLAN, with early onset of psychomotor regression, hypotonia, pyramidal and cerebellar signs, and abnormal ocular movements. The phenotype was highly homogeneous, with rapid development of severe spastic tetraparesis, cognitive impairment and optic atrophy. Neuroimaging showed cerebellar atrophy and claval hypertrophy to be the commonest and earliest signs, whilst cerebellar cortex hyperintensity and pallidal iron deposition were later findings. Motor or sensory-motor neuropathy and electroencephalogram fast rhythms were also frequent. Nine patients from six families shared the same founder mutation (p.V691del) which probably arose by the late seventeenth century. Only one patient fitted the diagnosis of the much rarer childhood-onset PLAN. Despite the early onset (18 months), clinical progression was slower, with behavioral disturbances and dystonia. Typical features of infantile-onset PLAN such as hypotonia, nystagmus/strabismus, optic atrophy, electroencephalogram fast rhythms and motor neuropathy were absent. Cerebellar atrophy, claval hypertrophy and pallidal hypointensity were evident at brain magnetic resonance imaging. This patient carried a missense variant predicted to be less deleterious. CONCLUSIONS: The PLAN-associated phenotypes and the challenges of diagnosing the childhood-onset form are delineated, and a common North African founder mutation is identifed.

Evolutionary patterns of the mitochondrial genome in Metazoa: exploring the role of mutation and selection in mitochondrial protein coding genes.

The mitochondrial genome is a fundamental component of the eukaryotic domain of life, encoding for several important subunits of the Respiratory Chain, the main energy production system in cells. The processes by means of which mtDNA replicates, expresses itself and evolves have been explored over the years, although various aspects are still debated. In this review, we present several key points in modern research on the role of evolutionary forces in affecting mitochondrial genomes in Metazoa. In particular, we assemble the main data on their evolution, describing the contributions of mutational pressure, purifying and adaptive selection, and how they are related. We also provide data on the evolutionary fate of the mitochondrial synonymous variation, related to the non-synonymous variation, in comparison with the pattern detected in the nucleus. Elevated mutational pressure characterises the evolution of the mitochondrial synonymous variation, whereas purging selection, physiologically due to phenomena such as cell atresia and intracellular mtDNA selection, guarantees coding sequence functionality. This enables mitochondrial adaptive mutations to emerge and fix in the population, promoting mito-nuclear coevolution.