Do I Need SMA Testing After Normal Amniocentesis Results?

Inquire about spinal muscular atrophy?

Hello, doctor.
I would like to ask a question.
I underwent amniocentesis, and after reviewing the report, my obstetrician informed me that the chromosomes are normal.
Do I still need to undergo testing for Spinal Muscular Atrophy (SMA)?

maggie, 30~39 year old female. Ask Date: 2012/10/23

Dr. Liu Yuhong reply Obstetrics and Gynecology

Spinal muscular atrophy (SMA) is a selective item in prenatal screening.
Amniocentesis, which can be performed or not, does not include genetic testing for spinal muscular atrophy.
Normal chromosomal results from amniocentesis are unrelated to whether the fetus has spinal muscular atrophy.

Reply Date: 2012/10/23

More Info

After receiving normal results from an amniocentesis, the decision to proceed with additional testing, such as Spinal Muscular Atrophy (SMA) screening, largely depends on several factors, including family history, ethnic background, and specific concerns regarding genetic conditions.

Amniocentesis is a prenatal diagnostic procedure that involves extracting a small amount of amniotic fluid surrounding the fetus to analyze its genetic material. This test is primarily used to detect chromosomal abnormalities, such as Down syndrome or other genetic disorders. If the results indicate that the chromosomes are normal, it suggests that major chromosomal abnormalities are unlikely.

However, SMA is a genetic disorder caused by mutations in the SMN1 gene, which leads to the degeneration of motor neurons and can result in muscle weakness and atrophy. SMA is inherited in an autosomal recessive manner, meaning that both parents must carry a copy of the mutated gene for their child to be affected. Therefore, if there is a family history of SMA or if both parents are carriers of the SMN1 mutation, it is advisable to consider SMA testing even after normal amniocentesis results.

In the United States, SMA screening is becoming increasingly common as part of expanded carrier screening panels. These panels test for a variety of genetic conditions, including SMA, and can provide valuable information about the risk of passing on genetic disorders to offspring. If you or your partner have a family history of SMA or belong to an ethnic group with a higher carrier frequency (such as Ashkenazi Jewish descent), it may be prudent to undergo SMA testing.

Moreover, if you have any concerns about your baby's health or if there are any symptoms that suggest a genetic condition, discussing these with your healthcare provider is essential. They can provide personalized recommendations based on your specific situation and may suggest additional testing if warranted.

In summary, while normal amniocentesis results are reassuring regarding chromosomal abnormalities, the decision to pursue SMA testing should be based on family history, carrier status, and any specific concerns you may have. It is always best to have an open discussion with your healthcare provider to determine the most appropriate course of action for you and your baby.

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