Amyotrophic lateral sclerosis is one of the most serious neurodegenerative disease, leading to death in 3 years by progressive paralysis of 4 limbs, speech, swallowing and breathing, and due to a progressive death of central and peripheral neurons. The cause of the disease is unknown, but an immunologically factor is more precisely suspected in ALS. Since 2008, the work of Immunology have shown that vitamin D was a major regulator of immunity. It regulates particularly the function of dendritic cells and regulates the immune response in macrophages. A vitamin D deficiency will induce activation of microglia. In neurology, vitamin D deficiency is associated with a greater impairment in neuronal function. This deficit is associated with a faster alteration of the microvasculature, alteration known to increase neuronal suffering and to enhance the neurodegenerative processes. The investigators postulate that ALS patients have a more severe prognosis if their vitamin D levels at the time of diagnosis is lower. The main objective of this study is to investigate the correlation between the rate of motor decline and blood levels of Vitamin D total. Secondary objectives are to investigate the relationship between blood levels of vitamin D and total disease duration of ALS, forced vital capacity, weight loss, age of onset and the start site of ALS.