When it comes to the Ice Bucket Challenge, you’ll know exactly what the disease in question is – amyotrophic lateral sclerosis (, ALS), or what we often call acromegaly. However, if you mention his brother, spinal muscular atrophy (SMA), you must be confused, since 1891 by Werdning Down syndrome, that is, trisomy 21, also known as congenital stupidity or Down syndrome, is a disease caused by an extra chromosome 21. Chromosomes are substances that contain human genetic information. There are 23 pairs of normal chromosomes, the first 22 pairs are called autosomes and the 23rd pair is sex chromosome, which is the key substance to determine gender, except for these are autosomes, which are the same for both sexes. It has been reported for 124 years now, yet the public does not know much about it. In contrast, amyotrophic lateral sclerosis (ALS) is well known thanks to Stephen Hawking and the Ice Bucket Challenge, but don’t worry, after reading this article you’ll be sure to know all about spinal muscular atrophy (SMA). Spinal muscular atrophy is a disease in which the degeneration of anterior horn cells leads to synthetic muscle atrophy and weakness. In simple terms, the anterior horn cells are the commander and the muscles are the soldiers. Since the commander has a problem, there is no way to command the war, and the soldiers are in a mess and have no intention to fight, so they have to surrender. According to the age of onset and the degree of lesion, the disease has four brothers: the oldest, the second and the third is called the child type SMA, every 6,000-100,000 people will have the onset of one person, is the most common and most hated killer in infancy. The oldest four are better behaved, and the disease starts only when they are 20 to 30 years old or older. The deadly weapon of SMA is a gene called “survival of motor neuron” (SMN) – without oxygen, humans cannot breathe. Without oxygen, humans cannot breathe, and without it, motor neurons cannot survive. This weapon (gene) has two sisters – SMN1 and SMN2; SMN1 is the big sister, as long as she has problems, you can not skate around as you like. But the severity of the matter also depends on SMN2, the sad little sister. If she accidentally loses your bicycle, electric car (i.e. the encoded protein), you will not be able to go to many places (a significant portion of the protein cannot function). The more careless your little sister (SMN2) is, the more you can’t move. Schematic diagram of the human SMN1 gene, the SMN2 gene and the synthesized pre-mRNA. Deletion or mutation of the SMN1 gene occurs in patients with spinal muscular atrophy (SMA). Most of the synthesized SMN2 pre-mRNAs lack exon 7 due to a C-T base substitution at exon 6. The shortened SMN protein is unstable and non-functional. A small percentage of SMN2 pre-mRNA can produce a full-length mRNA containing exon 7, so the synthesized protein is unaltered in length and functional. Image from Kolb, Stephen J., and John T. Kissel. Archives of neurology, 2011. You may be wondering why you have watched so many people die in pain when you understand the motive and the way it kills. The truth of the matter is, however, that due to the limitations of technology, it is difficult for us to invent effective drugs for the treatment of muscle atrophy. Although research has also been conducted on the carelessness of the little sister (wrong shearing of SMN2), the effective experimental results are also limited to animal models. Therefore, prevention of SMA fetuses, early detection of SMA fetuses, and termination of pregnancy are the most effective methods to prevent this disease.