| Disease ID | Source | Name | Description |
| 253300 | OMIM | Spinal muscular atrophy 1 (SMA1) | A form of spinal muscular atrophy, a group of neuromuscular disorder characterized by degeneration of the anterior horn cells of the spinal cord, leading to symmetrical muscle weakness and atrophy. Autosomal recessive forms are classified according to the age of onset, the maximum muscular activity achieved, and survivorship. The severity of the disease is mainly determined by the copy number of SMN2, a copy gene which predominantly produces exon 7-skipped transcripts and only low amount of full-length transcripts that encode for a protein identical to SMN1. Only about 4% of SMA patients bear one SMN1 copy with an intragenic mutation. SMA1 is a severe form, with onset before 6 months of age. SMA1 patients never achieve the ability to sit. The disease is caused by variants affecting the gene represented in this entry. |
| 271150 | OMIM | Spinal muscular atrophy 4 (SMA4) | An autosomal recessive form of spinal muscular atrophy, a neuromuscular disorder characterized by degeneration of the anterior horn cells of the spinal cord, leading to symmetrical muscle weakness and atrophy. Onset is in adulthood, disease progression is slow, and patients can stand and walk. The disease is caused by variants affecting the gene represented in this entry. |
| 253400 | OMIM | Spinal muscular atrophy 3 (SMA3) | An autosomal recessive form of spinal muscular atrophy, a neuromuscular disorder characterized by degeneration of the anterior horn cells of the spinal cord, leading to symmetrical muscle weakness and atrophy. Onset is after 18 months. Patients develop ability to stand and walk and survive into adulthood. The disease is caused by variants affecting the gene represented in this entry. |
| 253550 | OMIM | Spinal muscular atrophy 2 (SMA2) | An autosomal recessive form of spinal muscular atrophy, a neuromuscular disorder characterized by degeneration of the anterior horn cells of the spinal cord, leading to symmetrical muscle weakness and atrophy. It has intermediate severity, with onset between 6 and 18 months. Patients do not reach the motor milestone of standing, and survive into adulthood. The disease is caused by variants affecting the gene represented in this entry. |