Amniotic fluid chip testing
Hello Doctor, I would like to ask if amniotic fluid chip testing can detect Duchenne Muscular Dystrophy (DMD)? I found information online stating that this condition only occurs in males, as females have two X chromosomes that can compensate for each other, so they do not develop the disease.
If a girl is born, there is a 1 in 1500 chance of being a carrier; if a boy is born, there is a 1 in 3000 chance of inheriting the defective X chromosome from the mother.
Since the newborn screening for DMD requires a retest and it is a male baby, I am very concerned about the possibility of him having this disease.
Thank you for taking the time to respond, I appreciate it.
Enen, 30~39 year old female. Ask Date: 2022/03/01
Dr. Jian Yingxiu reply Rare Disease
Hello: I apologize for causing you concern.
This question can be answered in two parts:
1.
Can amniotic fluid chips detect DMD? Answer: Currently, the amniotic fluid chips available on the market that claim to detect DMD are likely only able to identify certain types of DMD.
The genetic mutations associated with DMD can be categorized into large deletions or duplications of gene sequences (which account for approximately 70% or more), and small deletions, duplications, or point mutations.
Large deletions or duplications can generally be confirmed through amniotic fluid chip testing.
However, point mutations require sequencing analysis, which cannot be detected by the chip.
2.
Should I be concerned about DMD if the newborn's out-of-pocket screening for DMD indicates a need for retesting? Answer: The out-of-pocket screening for DMD in newborns measures the levels of creatine phosphokinase (CPK or CK) in the baby's blood after birth.
Elevated levels of CPK can occur in DMD and other muscle disorders, but it is more commonly due to muscle compression experienced during birth, leading to a temporary increase.
Based on our experience, about 1-2% of newborns may be advised to undergo retesting due to elevated levels.
After the first retest, only 2% of those will require a second retest.
Among the children needing a third test, only three have been confirmed as patients.
However, due to case reports from abroad indicating that the initial values were not extremely abnormal, the screening process adopts a more conservative approach to ensure that any suspicious cases undergo further verification.
In summary, a normal amniotic fluid chip result significantly reduces the likelihood of a DMD diagnosis, but strictly following the newborn screening procedures can better ensure the baby's condition is monitored and prevent any missed diagnoses.
Reply Date: 2022/03/01
More Info
Amniotic fluid chip testing, often referred to as non-invasive prenatal testing (NIPT), has gained popularity for its ability to detect various genetic conditions in the fetus. One of the conditions that parents may be concerned about is Duchenne Muscular Dystrophy (DMD), a severe genetic disorder that primarily affects males due to its X-linked recessive inheritance pattern.
To address your question, while some amniotic fluid chip tests can screen for certain genetic disorders, the detection of DMD specifically can be complex. DMD is caused by mutations in the dystrophin gene located on the X chromosome. The majority of mutations leading to DMD are large deletions or duplications of the gene, which can be detected through certain types of genetic testing, including some amniotic fluid tests. However, smaller mutations, such as point mutations or small insertions/deletions, may not be detected by these tests. Therefore, while an amniotic fluid chip test may provide some information regarding the risk of DMD, it may not be comprehensive enough to rule it out entirely.
Regarding the statistics you mentioned, it is indeed true that DMD predominantly affects males, with a carrier female having a 1 in 1500 chance of being a carrier and a male child having a 1 in 3000 chance of being affected if the mother is a carrier. This highlights the importance of genetic counseling and testing for families with a history of DMD or related muscular dystrophies.
If the newborn screening for DMD indicated a need for further testing, it is understandable to feel anxious, especially since the child is male. The initial screening often measures creatine phosphokinase (CPK) levels, which can be elevated in conditions like DMD. However, elevated CPK levels can also occur due to other reasons, such as muscle trauma during birth, which is common and usually temporary. In fact, it is reported that about 1-2% of newborns may have elevated CPK levels at birth, and only a small percentage of those will require further testing.
If your healthcare provider has recommended a follow-up test, it is crucial to adhere to this advice. The follow-up will help clarify whether there is a genuine concern regarding DMD or if the initial results were due to benign factors. Genetic testing can provide definitive answers and is essential for understanding the child's health and any potential future implications.
In summary, while amniotic fluid chip testing can provide valuable information, it may not be sufficient for a definitive diagnosis of DMD. If there are concerns about the results of newborn screening, further genetic testing and consultation with a genetic counselor or specialist in pediatric neurology may be warranted. This will ensure that you have all the necessary information to make informed decisions about your child's health and any potential interventions that may be needed.
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