Microdeletions are a topic of extensive genetic research. These small deletions in the DNA sequence of a chromosome can have significant implications on an individual’s health. In this comprehensive blog post, we delve into the causes, risk factors, ten most common types of microdeletions, their prevalence, and the role of Non-Invasive Prenatal Testing (NIPT) in their detection.

What are Microdeletions?

Microdeletions are tiny losses of genetic material in the DNA sequence of a chromosome. These minute changes are typically undetectable under a standard microscope, hence the term ‘micro’. However, despite being minute, these deletions can lead to significant health and developmental problems, as they may disrupt several genes essential for growth and development.

Causes and Risk Factors

The exact cause of microdeletions remains unknown, and their occurrence seems largely spontaneous. They typically occur during the formation of reproductive cells or in early foetal development, resulting from a mistake in the cell’s DNA replication process.

In terms of risk factors, there’s no established link between microdeletions and parental age, ethnicity, or lifestyle. These changes can happen in any pregnancy, but familial history can increase the chances if a parent has a balanced translocation or an inherited microdeletion.

The Ten Most Common Microdeletion Syndromes

Here’s a list of ten of the most common microdeletion syndromes, along with their estimated prevalence:

Microdeletions, in general, occur in approximately 1 in every 1,000 births, making them a significant contributor to genetic disorders. Just to compare Down’s Syndrome, the most common chromosomal disorder affects approximately 1 in 1,000 to 1 in 1,100 live births worldwide. The frequency of Down’s Syndrome increases significantly with the mother’s age, particularly from 35 years onwards whereas microdeletions are believed to occur randomly.

Microdeletion Screening: The Role of NIPT

Screening for microdeletions has been revolutionised by advancements in genetic testing, particularly with the introduction of Non-Invasive Prenatal Testing (NIPT). This screening test, performed from the 10th week of pregnancy, analyses cell-free DNA in the maternal blood to identify common chromosomal abnormalities and microdeletions. NIPT poses no risk to the foetus and offers a safer alternative to invasive diagnostic procedures.

Though NIPT has high accuracy rates, it’s crucial to understand that a ‘positive’ result indicates an increased risk, not a definitive diagnosis. Positive NIPT results should always be confirmed through diagnostic tests such as amniocentesis or chorionic villus sampling (CVS).

There are a number of NIPT providers who offer screening for microdeletions, such as Panorama NIPT, Unity NIPT and PrenatalSAFE.

Conclusion

While the world of microdeletions might seem complex, understanding them is crucial to advancing our knowledge of genetic disorders. Early detection, made possible by advanced screening methods like NIPT, allows for better preparation and potential intervention. As research continues to evolve, we can hope for even more effective detection and management of these genetic changes, ultimately leading to improved healthcare and patient outcomes.

Remember, if you have any concerns or questions about genetic disorders or prenatal testing, it’s always advisable to consult with a healthcare professional who can provide tailored advice based on your individual circumstances.

DiGeorge Syndrome, also commonly known as 22q11.2 deletion syndrome (or simply 22q del,) is a complex and multifaceted disorder that many people may not be aware of. This blog post aims to shed light on the causes and risk factors of DiGeorge Syndrome, discuss screening options such as Non-Invasive Prenatal Testing (NIPT), and compare its prevalence with conditions such as Down’s Syndrome.

Understanding DiGeorge Syndrome (22Q DEL)

DiGeorge Syndrome is a chromosomal disorder caused by the deletion of a small piece of chromosome 22, specifically on the q11.2 region. The deletion happens spontaneously during the formation of reproductive cells or in early fetal development. The primary cause of 22q del is unknown, and it typically isn’t inherited from the parents.

The syndrome is characterised by a wide range of potential symptoms, including heart defects, certain facial features, and learning difficulties.problems with immune system and other abnormalities. Unfortunately, 22q del syndrome is also associated with learning difficulties and psychiatric or behavioural problems like autism and schizophrenia. Due to its complex nature, different individuals affected may present a different set of symptoms, making it a highly variable condition.

Risk Factors

Although the exact cause of the chromosomal deletion leading to DiGeorge Syndrome is unknown, it’s not typically associated with the age of the parent, unlike some other genetic disorders. The occurrence appears to be mostly random, which means that all pregnancies, irrespective of familial history, have a minimal but real risk.

Screening for DiGeorge Syndrome: The Role of NIPT

Non-Invasive Prenatal Testing (NIPT) has emerged as an invaluable tool for the early detection of several genetic disorders, including DiGeorge Syndrome. NIPT analyses cell-free DNA in the maternal blood to detect common chromosomal abnormalities. This test can be performed from the 10th week of pregnancy and poses no risk to the fetus.

While NIPT is highly accurate for detecting common trisomies like Down’s Syndrome (trisomy 21), Edwards’ syndrome (trisomy 18), and Patau’s syndrome (trisomy 13), it’s also valuable for identifying deletions like those causing DiGeorge Syndrome. It’s essential to remember, however, that a positive NIPT result for DiGeorge syndrome should be confirmed with diagnostic tests like amniocentesis or chorionic villus sampling (CVS) for a definitive diagnosis.

Not all NIPT provider offer reliable screening for DiGeorge Syndrome. Recently, the Panorama AI NIPT demonstrated impressive clinical performance for screening Di George Syndrome, you can read more about the study here. In well-designed prospective study Panorama Test was able to detect more than 80% of the fetuses affected by 22q del, showing an outstanding 50% positive predicted value.

Prevalence of DiGeorge Syndrome vs Down’s Syndrome

DiGeorge Syndrome is considered one of the most common genetic syndromes, second only to Down’s Syndrome. In the general population, it’s estimated to affect between 1 in 2,000 to 1 in 4,000 live births. Younger women have the same chance to deliver baby with 22q del as older ones.

In contrast, Down’s Syndrome, the most common chromosomal disorder, has a higher prevalence rate, affecting approximately 1 in 1,000 to 1 in 1,100 live births worldwide. The frequency of Down’s Syndrome increases significantly with the mother’s age, particularly from 35 years onwards.

Conclusion

Understanding and awareness of genetic disorders like DiGeorge Syndrome are crucial, not just for healthcare professionals, but for the general public too. While DiGeorge Syndrome is less common than Down’s Syndrome, it still represents a significant proportion of genetic disorders. By employing advanced screening methods such as NIPT, early detection and management of these conditions can be made possible.

Remember, if you have concerns or questions about genetic disorders or prenatal testing, it’s always best to consult with a healthcare professional who can provide advice tailored to your individual circumstances.

Summary:

The best NIPT will be really good at detecting problems (high sensitivity) and correctly saying everything is fine (high specificity). It should hardly ever make mistakes by saying there’s a problem when there isn’t (low false positive) or missing a problem and saying everything is okay (low false negative). If the test says there’s an issue, it should be highly likely to be true (high positive predictive value). And if it says everything is fine, it should be trustworthy (high negative predictive value).

NIPT (non-invasive prenatal testing) is a type of genetic test used to screen for certain chromosomal abnormalities and genetic syndromes in a developing fetus. The test involves analyzing a sample of the mother’s blood to look for fragments of DNA from the fetus.

It’s good to know the statistical terms related to NIPT performance because they help you understand how accurate the test is and what the results mean. You might be wondering why it’s important to understand those “boring statistics” related to NIPT (non-invasive prenatal testing) performance, but trust us, it’s actually really helpful! Knowing these statistical terms can make a big difference in your pregnancy journey.

By understanding these terms, you can make informed choices about your prenatal care. If the test is really accurate, you might feel more confident in the results and decide not to have further tests. But if the test has limitations, you might want to consider additional testing to get more clarity. It’s all about making sure you have the information you need to make the best choices for you and your baby.

So, while statistics might seem boring at first, they play a vital role in your understanding of the test’s accuracy, interpretation of results, and decision-making process. Embracing these statistics can give you more confidence and peace of mind throughout your pregnancy journey.

Please see below the most important statistical terms related to NIPT performance:

1. Sensitivity: This measures how good the test is at correctly identifying fetuses that have a chromosomal abnormality. A high sensitivity means that the test is good at detecting most cases of abnormality. For example, if a test has a sensitivity of 99%, it means that out of 100 fetuses with a chromosomal abnormality, the test correctly identifies 99 of them.
2. Specificity: This measures how good the test is at correctly identifying fetuses that do not have a chromosomal abnormality. A high specificity means that the test avoids identifying normal fetuses as abnormal. For example, if a test has a specificity of 99%, it means that out of 100 normal fetuses, the test correctly identifies 99 of them as normal.
3. Positive predictive value (PPV): This is the probability that a positive test result is a true positive. In other words, if the test comes back positive, the PPV measures the likelihood that the fetus actually has a chromosomal abnormality. For example, if a test has a PPV of 95%, it means that out of 100 positive test results, 95 of them are true positives.
4. Negative predictive value (NPV): This is the probability that a negative test result is a true negative. In other words, if the test comes back negative, the NPV measures the likelihood that the fetus does not have a chromosomal abnormality. For example, if a test has an NPV of 99%, it means that out of 100 negative test results, 99 of them are true negatives.
5. False positive rate (FPR): This measures how often the test gives a positive result for a normal fetus. A low FPR means the test is good at avoiding false positives. For example, if a test has an FPR of 1%, it means that out of 100 normal fetuses, the test gives a false positive result for only 1 of them.
6. False negative rate (FNR): This measures how often the test gives a negative result for an abnormal fetus. A low FNR means the test is good at avoiding false negatives. For example, if a test has an FNR of 1%, it means that out of 100 fetuses with a chromosomal abnormality, the test gives a false negative result for only 1 of them.

When we look at how well NIPT works, it’s important to consider a bunch of statistics together. A good test will have high sensitivity, high specificity, low false positive and false negative rates, and high PPV and NPV.

Just remember, the performance of NIPT can vary depending on the specific test and the group of people being tested. So, when you get the results, make sure to understand how good that particular test is.

Considering all these statistics helps us know how reliable the test is and what the results mean for you and your baby. It’s about making informed choices and getting the best care possible.

Learn more about the NIPT providers we use:

Harmony Test by Roche: https://harmonytest.roche.com/global/en/home.html

Panorama Test by Natera: https://www.natera.com/womens-health/panorama-nipt-prenatal-screening/

PrenatalSAFE by Eurofins: https://www.eurofins.ie/biomnis/our-services/medical-testing/non-invasive-prenatal-test-nipt-prenatalsafe/

Unity Test by BillionToOne: https://unityscreen.com/