In the previous article we talked about the diagnostic criteria for type 1 neurofibromatosis (the dermatologists at BYUH will teach you to diagnose your baby for neurofibromatosis yourself), and since these criteria are only evident for multiple milk café au lait spots from birth to 2 years of age, while most other clinical manifestations will develop later (e.g., axillary freckles and iris lipped nodules will mostly appear gradually after 5 years of age). Add to this the fact that nearly half of the patients with neurofibromatosis (type 2 may be higher) have no family history, and one can imagine the apprehension and agitation of parents with multiple café-au-lait spots in infancy, especially those larger than 3 (normal people can have <=3< span=""> café-au-lait spots). At this time, even if one goes to the most experienced doctor, the advice given is often non-deterministic (e.g. “…more likely” “…cannot be completely excluded”). Many parents continue to ask, “What tests do I need to do to be 100% sure that my child has neurofibromatosis? There is indeed a way to do this, and that is to perform genetic testing.
Although many times at the request of the parents, some doctors will put them in touch with a third party testing company (there are many such companies, over 10 in Beijing alone, and it can be a mixed bag). However, these companies sometimes give a completely ambiguous report (this is because they may not understand the meaning of certain results and therefore pass on the detected genetic variants to the patient without analysis), and since many doctors are not trained in genetic testing and report interpretation (genetic testing has advanced rapidly in recent years and many doctors’ knowledge is stuck in the 1990s), such reports often leave the parents with a more ambiguous report. Such reports often cause parents to become more confused and anxious, such as the following report from a well-known domestic testing company.
Such a report actually gives the result that NF1 is not detected as a pathogenic locus, which means that the test results suggest a high probability of being normal. However, it is clearly inappropriate to list a variant (also called genetic polymorphism, which does not cause disease and is a normal variant of DNA) that exists in a normal person to parents who have no medical expertise at all, and not to give a clear conclusion. A similar situation occurred in a patient (also one of my patients) who thought he had segmental neurofibromatosis, as follows (borrowing a photo example from the NEJM journal)
Such a patient had a mosaic type (mosacism) of neurofibromatosis, and the testing company recommended that the doctor take a blood test, which naturally came back negative as expected, but on the basis of which it was concluded that it was not neurofibromatosis and would not be inherited by the offspring, which is clearly wrong and extremely dangerous. Since genetic testing is a relatively expensive test, and the interpretation of genetic test results is a highly technical task (requiring strong background knowledge of genetics and the corresponding disease), it is always recommended to choose a doctor with relevant experience to recommend and prescribe the test.
So what why do we need genetic testing for neurofibromatosis? And if genetic testing is needed, when and how is it best to perform it?
1. Why genetic testing for neurofibromatosis?
Genetic testing is the gold standard for the diagnosis of all genetic skin diseases, including neurofibromatosis. Therefore
The significance of testing for patients with neurofibromatosis cannot be overstated. The main benefits are as follows.
(1) Genetic testing for multiple café-au-lait spots in infants and children can help to confirm or exclude the diagnosis of neurofibromatosis at an early stage, thus intervening early or avoiding unnecessary anxiety.
(2) If high-throughput gene sequencing can be performed, it can also identify other diseases that may be associated with café-au-lait spots, such as tuberous sclerosis, Legius syndrome, etc. We once tested an outpatient who had been suspected of having neurofibromatosis and the result was Legius syndrome (a type 1 neurofibromatosis disease that basically does not grow tumors). The patient was relieved of his psychological doubts and fears and decided to live as normal without additional intervention. Quality of life was significantly improved
(3) Genetic diagnosis of patients identified as having neurofibromatosis allows for accurate genetic counseling for members of the family, i.e., to determine the probability of informing family members of the inheritance of neurofibromatosis in their offspring and to clarify which members need to undergo prenatal diagnosis.
(4) Perform accurate prenatal diagnosis. For fetuses at risk of recurrence, chorionic villus or amniocentesis is performed to confirm the diagnosis for the fetus in advance, which helps the family to deliver healthy offspring. Also, the rapid development of IVF + preimplantation prenatal diagnosis technology is expected to provide inexpensive, safe, and accurate preimplantation prenatal diagnosis to patient families in the future, ensuring that families at risk will produce healthy babies.
It should be noted that finding the locus of the genetic defect is not yet helpful for a complete cure of neurofibromatosis. Pending advances in medicine and science, targeted gene therapy based on the identification of genetic defects may be expected in the future.
2. When to perform genetic testing for neurofibromatosis
Theoretically, genetic testing can be done at any time. However, there are several special groups of people for whom genetic testing may have special timing.
(1) A family member has a request to have another child. If a family member has a request to have another child, early genetic diagnosis is recommended. It is better to have the genetic diagnosis of the patients in the family done before pregnancy, so that the prenatal diagnosis can be done comfortably during pregnancy, to avoid the pregnancy week is too big to have prenatal diagnosis.
(2) The distribution of café au lait spots is unilateral or segmental. As shown below, if the distribution of café au lait spots is obviously asymmetrical, it is very likely that the genetic test will not be able to detect the results. In this case, we need to wait until the tumor is present, and then take the tumor and blood for testing at the same time, in order to get an accurate result.
3.How to perform genetic testing for neurofibromatosis
This should be a matter for doctors to consider. However, given the varying levels of doctors in China and the complete lack of understanding of clinical disease by genetic testing companies, I think it is better for patients and their families to understand this matter.
(1) Selection of the test specimen: Normally, genetic testing for monogenic genetic diseases is performed by blood collection (or in a few cases, by collecting saliva or oral brush to remove epithelial cells) for DNA extraction. Some patients with neurofibromatosis are very specific, such as the segmental neurofibromatosis and the unilateral distribution of neurofibromatosis we see above. It is very likely that the genetic mutation will not be found when blood is taken in this case. In these patients, the mutation does not originate from the germ cells (sperm or egg), but rather the disease is caused by a mutation in the NF1 gene that occurs in one cell after the syncytium (that is, the germ cells have combined to become an embryo) has divided to a certain level of cell number. As shown in the figure below, if the embryonic cells that developed NF1 did not differentiate into blood cells later, you will not be able to detect the mutation in the blood, but the mutation does exist in the skin and nerve tissue. At this time, it is important to take the tumor for testing, otherwise the results will be biased, resulting in a negative result when the disease was present. In addition, genetic testing without the collection of parental specimens for testing is not a formal practice and may result in incorrect results.
(2) Choice of test method: NF1 and NF2, the causative genes of neurofibromatosis, have a higher incidence of deletion of large segments than other genes. This condition cannot be detected using conventional genetic testing methods and must be detected using a test called MLPA. Therefore, it is recommended that in cases where the test is negative, additional testing for MLPA must be done, otherwise the diagnosis may be missed. For patients who show multiple caffeinated spots, we recommend testing the genes of common diseases that may occur in caffeinated spots together, including common tuberous sclerosis, Legius syndrome, etc.
(3) Interpretation of genetic test results: This is the most difficult one. Many genetic test companies only use software to compare and predict, which is not scientific. Recently the parents of a typical neurofibromatosis patient came to me with a very typical clinical presentation of their child, including multiple coffee spots, axillary freckles, neurofibromatosis bodies, and mild cognitive impairment. The parents wanted to have a second child and came to me for a prenatal diagnosis, but their previous doctor recommended that they spend $5,000 on testing with a company that told them that the child had no mutations in the NF1 gene. After I contacted the company to pull over the original sequencing data, I found that the child had the following mutations in the NF1 gene.
NF1
29527613
SNP
G
het
G/A
114/74
p.K354K
The genetic testing company considered this to be a normal variant site that is not pathogenic, reasoning that the amino acids of the patient are not altered after the nucleotide mutation (p.K354K), which is true in 99% of cases. However, after careful comparison, I found that this site is located in the last nucleotide of the exon, and this mutation does not change the amino acid, but it affects the protein shear, which can also lead to serious consequences. Later we confirmed by our own validation method that this locus is the pathogenic mutation in the child and successfully provided them with a prenatal diagnosis and a healthy baby was born. Therefore, the results of the test must be judged by an experienced physician, and the reports of genetic testing companies should not be completely trusted.
In summary, genetic testing for neurofibromatosis is a powerful tool to confirm the diagnosis of the disease and can bring definitive answers to the diagnosis of the disease, prenatal diagnosis, and even the choice of treatment. But before undergoing genetic testing, be sure to ask these three questions first. Caution is advised if the doctor who prescribes the test to you is unable to provide you with satisfactory answers to questions such as the three above, and instead refers you to a random genetic testing company for testing.