Spinal muscular atrophy is the second most common fatal single-gene disease, second to thalassemia major. The progressive degeneration of the anterior horn cells (motor neurons) of the spinal cord causes muscle paralysis, atrophy and weakness, but the patient is completely normal in intelligence.

Spinal muscular atrophy is classified into three types according to the age of onset, the severity of the disease and the degree of muscle affected. The first is severe type, usually infants (before 2 years old) will die of respiratory failure; the third is mild type, manifested by mild muscle weakness in the proximal extremities, in which patients can usually survive for a long time; and the second type is between the two regarding severity.

Will my baby inherit spinal muscular atrophy?

• The disease is an autosomal recessive genetic disorder in which one in 40 people in Taiwan is the carrier. The carrier does not show any clinical symptoms, so it cannot be detected by the patient. Even the regular blood test does not have abnormal results, which can only be identified by genetic diagnosis.
• If the parents are both carriers, they have 25% chance of having a child with SMA for each pregnancy.(see the figure next page). On average, one in 4,000 to 10,000 newborns born with the disease.

Subjects and methods of genetic testing for spinal muscular atrophy

• Now we can quickly and accurately screen out the carriers, with sensitivity up to 95%. It is recommended that every couple with planned parenthood, after marriage or pregnancy, undergo genetic testing for SMA carriers.
• The exam is a blood test which costs NT$2,200. If you have decided to receive amniocentesis, you can also have a small sample of amniotic fluid taken for gene detection of spinal muscular atrophy of the fetus, at your own expense of NT$3,000.

How do I get the test results?

• You can get the report in 2 weeks after blood test (or 3 weeks for amniotic fluid sampling). If the carrier is identified, we will inform you by telephone and offer genetic counseling and further conduct the genetic testing of your husband.

Genetic patterns of spinal muscular atrophy

• Carrier rate: 1/40