Muscle biopsy – Generally, diagnosis is made through a muscle biopsy. A sample of muscle is taken, and examined under a microscope. This is done in one of two ways: either a small piece of muscle is taken under general anaesthetic or a needle biopsy is performed to remove a small sample. Muscle from people affected by nemaline myopathy has a distinctive pattern with thin thread- or rod-like structures in the muscle cells. It is important to note that these structures are also seen in other, unrelated conditions. For this reason, the muscle sample must be considered along with the physical signs and/or molecular tests, in order for a diagnosis of nemaline myopathy to be made. See our factsheet on muscle biopsies.
Molecular testing – In families where the mutation is known to occur in the gene for α- actin, molecular testing is available. This involves taking a blood sample and analysing the DNA for the presence of a mutation. The gene is ‘read’ from end to end, and this sequence is compared to a normal α- actin sequence. This process can take several weeks to complete. Once this error has been identified in one family member, it is possible to use this sequence to diagnose other family members.
Prenatal diagnosis – Prenatal diagnosis is available for families where the mutation has been identified as being in the gene for α- actin, and the precise nature of the mutation established. The technique is described in the section ‘Molecular testing’, but there are two ways to obtain samples for testing:
- Amniocentesis is traditionally performed at 15 to 17 weeks into the pregnancy. Using ultrasound to visualise, a needle is inserted through the abdominal wall, and a sample of the fluid surrounding the baby (amniotic fluid) is taken.
- Chorionic villus sampling (CVS) is carried out at 10 to 11 weeks. This involves taking a sample of tissue from the placenta. Results are available earlier using this technique than amniocentesis, but the rate of spontaneous abortion is slightly higher.
Carrier testing – As with prenatal diagnosis, carrier testing is currently only available for families where a mutation in the α- actin has been identified and characterized.