Expression profiling reveals multiple myelin alterations in murine succinate semialdehyde dehydrogenase deficiency.

Succinic semialdehyde dehydrogenase (SSADH) deficiency, a rare genetic defect of GABA degradation recently modelled in mice (SSADH(-/-) mice), manifests early absence seizures that evolve into generalized convulsive seizures and lethal status epilepticus in gene-ablated mice. Disrupted GABA homeostasis, in conjunction with the epileptic phenotype and increased gamma-hydroxybutyric acid (GHB), suggested that expression profiling with the U74Av2 Affymetrix system would reveal dysregulation of receptor genes associated with GABAergic and glutamatergic neurotransmission. Unexpectedly, we found significant downregulation for genes associated with myelin biogenesis and compaction, predominantly in hippocampus and cortex. These results were confirmed by: (1) myelin basic protein (MBP) immunohistochemistry; (2) western blotting of myelin-associated glycoprotein (MAG) and MBP; (3) qRT-PCR analyses of myelin-associated oligodendrocytic basic protein (MOBP), MAG, MBP and proteolipid protein (PLP) in hippocampus, cortex and spinal cord; (4) quantitation of ethanolamine and choline plasmalogens, all core myelin components; (5) evaluation of myelin content in brain sections employing toluidine blue staining; and (6) ultrastructural evaluation of myelin sheath thickness via electron microscopy. We speculate that increased GABA/GHB, acting through GABAergic systems, results in decreased levels of the neurosteroids progesterone and allopregnanolone [Gupta et al (2003) Ann Neurol 54(Supplement 6): S81-S90] and phosphorylation of mitogen-activated protein (MAP) kinase, with resulting myelin protein abnormalities primarily in the cortex of SSADH(-/-) mice.

Cognitive dysfunction in NF1 knock-out mice may result from altered vesicular trafficking of APP/DRD3 complex.

BACKGROUND: It has been estimated that more than 50% of patients with Neurofibromatosis type 1 (NF1) have neurobehavioral impairments which include attention deficit/hyperactivity disorder, visual/spatial learning disabilities, and a myriad of other cognitive developmental problems. The biological mechanisms by which NF1 gene mutations lead to such cognitive deficits are not well understood, although excessive Ras signaling and increased GABA mediated inhibition have been implicated. It is proposed that the cognitive deficits in NF1 are the result of dysfunctional cellular trafficking and localization of molecules downstream of the primary gene defect. RESULTS: To elucidate genes involved in the pathogenic process, gene expression analysis was performed comparing the expression profiles in various brain regions for control and Nf1+/- heterozygous mice. Gene expression analysis was performed for hippocampal samples dissected from postnatal day 10, 15, and 20 mice utilizing the Affymetrix Mouse Genome chip (Murine 430 2.0). Analysis of expression profiles between Nf1+/- and wild-type animals was focused on the hippocampus because of previous studies demonstrating alterations in hippocampal LTP in the Nf1+/- mice, and the region's importance in visual/spatial learning. Network analysis identified links between neurofibromin and kinesin genes, which were down regulated in the Nf1+/- mice at postnatal days 15 and 20. CONCLUSION: Through this analysis, it is proposed that neurofibromin forms a binding complex with amyloid precursor protein (APP) and through filamin proteins interacts with a dopamine receptor (Drd3). Though the effects of these interactions are not yet known, this information may provide novel ideas about the pathogenesis of cognitive defects in NF1 and may facilitate the development of novel targeted therapeutic interventions.

Mapping of sudden infant death with dysgenesis of the testes syndrome (SIDDT) by a SNP genome scan and identification of TSPYL loss of function.

We have identified a lethal phenotype characterized by sudden infant death (from cardiac and respiratory arrest) with dysgenesis of the testes in males [Online Mendelian Inheritance in Man (OMIM) accession no. 608800]. Twenty-one affected individuals with this autosomal recessive syndrome were ascertained in nine separate sibships among the Old Order Amish. High-density single-nucleotide polymorphism (SNP) genotyping arrays containing 11,555 single-nucleotide polymorphisms evenly distributed across the human genome were used to map the disease locus. A genome-wide autozygosity scan localized the disease gene to a 3.6-Mb interval on chromosome 6q22.1-q22.31. This interval contained 27 genes, including two testis-specific Y-like genes (TSPYL and TSPYL4) of unknown function. Sequence analysis of the TSPYL gene in affected individuals identified a homozygous frameshift mutation (457_458insG) at codon 153, resulting in truncation of translation at codon 169. Truncation leads to loss of a peptide domain with strong homology to the nucleosome assembly protein family. GFP-fusion expression constructs were constructed and illustrated loss of nuclear localization of truncated TSPYL, suggesting loss of a nuclear localization patch in addition to loss of the nucleosome assembly domain. These results shed light on the pathogenesis of a disorder of sexual differentiation and brainstem-mediated sudden death, as well as give insight into a mechanism of transcriptional regulation.