Molecular pathophysiology of amyotrophic lateral sclerosis (ALS): A novel approach for detection of biochemical perturbations in normal tissue

Amyotrophic Lateral Sclerosis (ALS) is the most common progressive neurological disorder of adults typically striking between the ages of 50–60 years. Selective degeneration of motor neurons leads to muscle atrophy and death 1–5 years after diagnosis.;Our goal was to investigate pathophysiology and genetic susceptibility of ALS using ALS patient's skeletal muscle. Our lab already identified biochemical pathways in Hereditary Spastic Paraplegia using skeletal muscle (Molon et al., 2004). The rationale is that most neurological disorders show systemic biochemical perturbations, and using pathologically normal tissue in affected individuals may prove superior in identifying altered biochemical pathways.;To identify biochemical perturbations in ALS muscle, we generated mRNA expression profiling data from skeletal muscle of five SALS patients. Data analyses conducted relative to 128 patients in 13 diagnostic disorders. Then novel bioinformatics approaches Leave-one out, Adaptive Individual Discriminatory Genes and a visual and statistical data analyzer algorithm generating a phenotypic tree classification were used to identify candidate genes specific for ALS. Three candidate transcripts Myocyte Enhancer Factor 2C (MEF2C), Flavin Containing Monooxygenase 3 (FMO3) and Spinocerebellar ataxia 1 (ATXN1) were specifically altered in ALS and validated in a second set of SALS muscle samples. To rule out non-specific response to denervation, transcripts were studied in a mouse model of denervation. QMF-RT-PCR was performed in a SOD1G93A murine model and we created hypothetical biochemical models linking FMO3, MEF2C and SCA1 to ALS.;The hypothesis that SNPs in FMO3, MEF2C or ATXN1 might predispose to ALS was tested using SNP discovery. One novel SNP was detected in MEF2C 3' UTR region (162de1[A]). Genotyping was performed on conserved, validated, promoter or nonsynonymous SNPs found in FMO3, MEF2C, ATXN1 in 86 ALS samples versus 96 controls. An association was found between ATXN1 SNP rs522591 with ALS in all subjects and in Caucasians (p-value = 0.04) and rs647750 was associated with ALS if dominant inheritance was assumed in all subjects (p-value = 0.02), and Caucasians (p-value = 0.01).;Our data suggests that polymorphisms in ATXN 1 may underlie some cases of sporadic ALS. Moreover, we have established candidate biochemical pathways that may drive the pathogenesis of sporadic ALS.