There are six sub-groups of nemaline myopathy, which are defined based on age of onset and severity of condition, although there is a high degree of overlap between the conditions. There does not seem to be a correlation between severity of the condition and the gene which has the mutation. Although heart problems are not common in people with a rod myopathy, it is important that cardiac function is regularly monitored.
The progression of these conditions is variable, and some may progress more quickly than others. Generally it is accepted that the earlier the onset, the more severe the condition. For children who live beyond the early years, only some will lose the ability to walk. Respiratory function is thought to improve over time, with the most severe problems occurring earlier in life.
Severe congenital form
- Onset at birth
- Severe floppiness and muscle weakness
- Little spontaneous movement
- Difficulties with sucking and swallowing
- Severe breathing problems
- Death usually occurs early
Amish nemaline myopathy
- Onset at birth
- Floppiness/hypotonia
- Contractures/tightening of joints
- Breathing problems
- Death usually within two years of life
Intermediate congenital form
- Onset at birth
- Severity in between severe and mild forms
- Early development of contractures/tightening of joints
- Delayed motor milestones
- Independent breathing at birth
- Use of ventilatory support and/or wheelchair by 11 years
Typical (mild) congenital form
- Onset between birth to one year
- Floppiness/hypotonia
- Weakness in muscles closest to trunk, and sometimes spreading to more distal muscles
- Feeding difficulties
- Some respiratory weakness, but less severe than other forms
Childhood-onset
- Onset between 8 and 15 years
- Early motor development normal
- Symmetrical weakness of ankle, including foot drop
- Slowly progressive weakness with eventual involvement of all ankle movement
- Motor development normal
Adult-onset
- Onset between 20 to 50 years
- Generalised weakness with rapid progression
- Muscle pain
- Sometimes severe neck weakness
- Usually no previous family history