The DUX4 gene at the FSHD1A locus encodes a pro-apoptotic protein.

Facioscapulohumeral muscular dystrophy (FSHD) patients carry contractions of the D4Z4-tandem repeat array on chromosome 4q35. Decrease in D4Z4 copy number is thought to alter a chromatin structure and activate expression of neighboring genes. D4Z4 contains a putative double-homeobox gene called DUX4. We identified DUX4 mRNAs in cells transfected with genomic fragments containing the DUX4 gene. Using RT-PCR we also recognized expressed DUX4 mRNAs in primary FSHD myoblasts. Polyclonal antibodies raised against specific DUX4 peptides detected the DUX4 protein in cells transfected with D4Z4 elements. DUX4 localizes in the nucleus of cells transfected with CMV-DUX4 expression vectors. A DUX4-related protein is endogenously expressed in nuclei of adult and fetal human rhabdomyosarcoma cell lines. Overexpression of DUX4 induces cell death, induces caspase 3/7 activity and alters emerin distribution at the nuclear envelope. We propose that DUX4-mediated cell death contributes to the pathogenic pathway in FSHD.

Brisk deep-tendon reflexes as a distinctive phenotype in an Argentinean spinocerebellar ataxia type 2 pedigree.

Slow saccades, postural/intention tremor, peripheral neuropathy, and decreased deep-tendon reflexes are valuable neurological signs for clinical suspicion of spinocerebellar ataxia type 2 (SCA2). We report the presence of abnormally brisk deep-tendon reflexes in nonsymptomatic carriers and mildly and severely affected subjects of a large Argentinean SCA2 pedigree. The identification of this distinctive SCA2 phenotype in an entire pedigree reinforces the current concept that clinical algorithms are of limited value as indicators for genetic testing in SCA. Combined with published pedigrees of SCA2 manifesting as levodopa-responsive parkinsonism, this finding suggests that modifier genes could influence the clinical phenotype of SCA2.

Correlation between synaptogenesis and the PTEN phosphatase expression in dendrites during postnatal brain development.

The PTEN (phosphatase and tensin homolog deleted on chromosome 10) tumor suppressor gene codifies a lipid inositol 3'-phosphatase that negatively regulates cell survival mediated by the phosphatidyl inositol 3' kinase (PIP3-kinase)--protein kinase B/Akt signaling pathway. Recently, PIP3-kinase was involved in axon polarization, but PTEN functions in dendrites are uncertain. Using amino-terminal antibodies against the catalytic domain, we found a 34 kDa fragment of PTEN protein detected only in mouse brain tissue, present in neuron dendrites and spines of cerebral cortex, cerebellum, hippocampus and olfactory bulb. The PTEN-fragment reaches the synaptic fraction with a positive temporal correlation with synaptic stabilization in postnatal cerebellum and brain. In the weaver mutant mice, PTEN was absent only in the Purkinje cells dendrites that cannot receive the granule cells synaptic input. Furthermore, the activated p-Akt/PKB was present in axons but not in dendrites of mature neuron cells. P-Akt was also altered by the weaver mutation maintaining the inverse correlation with the PTEN-fragment in Purkinje cell dendrites. In contrast, the expression of this fragment was not affected by the staggerer mutation. Together, these results suggest that synaptogenesis is a necessary process for polarization in PIP3 pathway mediated by the PTEN catalytic-fragment into dendrites of CNS neurons.

myotilin Mutation found in second pedigree with LGMD1A.

Limb-girdle muscular dystrophy 1A (LGMD1A [MIM 159000]) is an autosomal dominant form of muscular dystrophy characterized by adult onset of proximal weakness progressing to distal muscle weakness. We have reported elsewhere a mutation in the myotilin gene in a large, North American family of German descent. Here, we report the mutation screening of an additional 86 families with a variety of neuromuscular pathologies. We have identified a new myotilin mutation in an Argentinian pedigree with LGMD1 that is predicted to result in the conversion of serine 55 to phenylalanine (S55F). This mutation has not been found in 392 control chromosomes and is located in the unique N-terminal domain of myotilin, only two residues from the T57I mutation reported elsewhere. Both T57I and S55F are located outside the alpha-actinin and gamma-filamin binding sites within myotilin. The identification of two independent pedigrees with the same disease, each bearing a different mutation in the same gene, has long been the gold standard for establishing a causal relationship between defects in a gene and the resultant disease. As a description of the second known pedigree with LGMD1A, this finding constitutes that gold standard of proof that mutations in the myotilin gene cause LGMD1A.