Nemaline Myopathy 2 (NEB)
Nemaline myopathy 2 is an autosomal recessive neuromuscular disorder that is caused by pathogenic variants in the gene NEB. While it is found in different ethnicities around the world, it is more prevalent in individuals of Ashkenazi Jewish or Finnish descent due to the presence of founder mutations. This disorder is characterized by muscle weakness and the presence of rod-shaped structures (nemaline bodies or rods) in affected muscle fibers. The typical, and most common, form is characterized by the infantile onset of a slowly progressive or non-progressive weakness of facial, bulbar, and respiratory muscles and neck flexors. Initial weakness is primarily proximal, with later distal involvement. Patients usually have difficulty walking and cannot run, but many remain ambulatory into adulthood. Life expectancy may not be reduced. In the most severe form, which is less common, decreased fetal movements are noticed before birth, and patients will not achieve the ability to sit or walk. These patients also have joint contractures and difficulty breathing, and usually do not survive infancy. It is not currently possible to predict the severity of the disease based on the genotype.
For information about carrier frequency and residual risk, please see the residual risk table.