IGF1 and amyotrophic lateral sclerosis: But, years later, the same team revealed that circulatory IGF-1 is important for maintaining normal growth by the study that liver IGF-1 and ALS double knockout mice were much smaller because there was a decrease in not only IGF-1 production but also circulatory IGF-1 stability that originated from compensatory nonliver sources because of the absence of protective ALS protein [3].