The two most common gene mutations causing nemaline myopathy are found on "NEB" or "ACTA1". Mutations of the NEB gene usually result in symptoms present at birth or beginning in early childhood. This mutation results in about 50% of affected nemaline myopathy patients. The most common inheritance pathway for those with mutations in "NEB" is autosomal recessive in which each parent carries one mutated copy along with one normal functioning copy of the gene, and they pass the mutated copy to their offspring. In some cases, occasionally with "ACTA1" mutations, NM can be caused by an inheritance pattern of autosomal dominance. This mutation results in about 15 to 25 percent of NM cases. One reason why this is lower is because NM is associated with "de novo" mutations in "ACTA1", occurring spontaneously in the egg or sperm. When the condition is heritable, each pregnancy with the same partners has the same risk of passing the mutated genes to offspring. New mutations (de novo) can also occur causing NM and de novo mutations have been most often found to occur in the "ACTA1" gene.