Fetal akinesia deformation sequence and neuroaxonal dystrophy without PLA2G6 mutation

A novel type of familial proximal axonal dystrophy: three cases and a review of the axonal dystrophies

Three related infants of Roma ancestry, two of them siblings, showed hypotonia, predominantly axial, from birth, difficulty swallowing, myoclonic seizures, and respiratory difficulty. Dysmorphic features, principally micrognathia were present. EEGs showed focal epileptiform abnormalities. All three died in their 5th month from respiratory insufficiency complicated by pneumonia. Autopsy showed small brains without malformation. Microscopy revealed numerous axonal spheroids involving particularly the brain stem and spinal cord, with especial prominence in the middle cerebellar peduncle, the anterior part of the thalamic reticular nuclei, and the anterior horns and columns of the spinal cord. Spheroids that appeared to be on axons of lower motor neurons were especially large. No spheroids were seen in peripheral nerves; electron microscopy did not show spheroids in skin. By electron microscopy spheroids contained neurofilaments, sparse mitochondria, and electron dense granules. The material did not allow identification of microtubules. Closely packed vesicles excluded neurofilamanets from the center of many spheroids, especially in the middle cerebellar peduncle. Sprouting of axons from the surface of many spheroids was seen. This disease is distinct from the well described type of infantile neuroaxonal dystrophy (Seitelberger's disease) in view of the distribution of spheroids, presence of spheroids on proximal rather than distal parts of axons, sparing of the peripheral nerves, lack of staining for synuclein, presence of sprouting, and lack of membranous profiles in the spheroids. A review of reported types of axonal dystrophy has not shown identical cases.

Genetics of neurodegeneration with brain iron accumulation

The condition originally called Hallervorden-Spatz syndrome is a collection of related disorders involving abnormal iron accumulation in the basal ganglia, usually manifesting with a movement disorder. To date, mutations in the following genes have been associated with neurodegeneration with brain iron accumulation (NBIA) phenotypes: PANK2, PLA2G6, FA2H, ATP13A2, C2orf37, CP, and FTL. This collection, now classified under the umbrella term NBIA, continues to evolve as new genes and associated phenotypes are recognized. As this body of information continues to grow, better approaches to diagnosis and treatment have become available. Continued investigations of the underlying pathogenesis of disease, with a focus on lipid, iron, and energy metabolism, will lead to the identification of new therapeutic targets.

A novel mitofusin 2 mutation causes canine fetal-onset neuroaxonal dystrophy

We recently reported autosomal recessive fetal-onset neuroaxonal dystrophy (FNAD) in a large family of dogs that is not caused by mutation in the PLA2G6 locus (Fyfe et al., J Comp Neurol 518:3771-3784, 2010). Here, we report a genome-wide linkage analysis using 333 microsatellite markers to map canine FNAD to the telomeric end of chromosome 2. The interval of zero recombination was refined by single-nucleotide polymorphism (SNP) haplotype analysis to ~200 kb, and the included genes were sequenced. We found a homozygous 3-nucleotide deletion in exon 14 of mitofusin 2 (MFN2), predicting loss of a glutamate residue at position 539 in the protein of affected dogs. RT-PCR demonstrated near normal expression of the mutant mRNA, but MFN2 expression was undetectable to very low on western blots of affected dog brainstem, cerebrum, kidney, and cultured fibroblasts and by immunohistochemistry on brainstem sections. MFN2 is a multifunctional, membrane-bound GTPase of mitochondria and endoplasmic reticulum most commonly associated with human Charcot-Marie-Tooth disease type 2A2. The canine disorder extends the range of MFN2-associated phenotypes and suggests MFN2 as a candidate gene for rare cases of human FNAD.