|
Testing of Children Without Symptoms and Prenatal Diagnosis (1995) The onset of CMT is often in adolescence, allowing a period of time during childhood when those at risk are free of symptoms. With the discovery of DNA mutations in CMT 1A and X1, it is possible to do presymptomatic testing for young children. Parents may be curious to know their children's genetic status and wish to facilitate planning for the future of the child. Is there really and advantage for the child? There is currently no known treatment which might prevent or delay the onset of CMT. Presymptomatic testing could be disadvantageous for the child through alteration in the relationship with the parent, or brothers and sisters, a tendency to label the child as disabled before symptoms ever occur, and a negative impact on the self-esteem of the developing child. The DNA test cannot predict which symptoms will occur at the onset of CMT, the severity of symptoms over the course of a lifetime, or which symptoms the individual will manifest. DNA testing could negatively impact the child through discrimination in education and physical activity. There are also issues of insurance discrimination. Another issue to consider is request for DNA testing related to adoption. Both adoption agencies and adoptive parents might want to know the DNA status of a child. Such testing might not be in the best interest of the child who could be harmed by being more difficult to place. The ethical implications of prenatal diagnosis are particularly complex and controversial. It is theoretically possible to do prenatal testing using amniocentesis to determine whether or not a fetus will be affected with CMT 1A, although we know of no commercial laboratory doing the CMT 1A 17p duplication test for prenatal diagnosis. However, such testing would have limitations similar to those listed for presymptomatic testing. The test cannot predict the onset, severity, or nature of symptoms. There is no particular benefit for knowing prenatally whether or not a child will be born with CMT. It does not change treatment of that child at birth or predict any known symptoms in the newborn. The purpose of prenatal testing is to enable termination of pregnancy if the fetus is known to be affected. This is not a consideration for most families because CMT does not cause early death, mental retardation, seizures, blindness, or congenital malformations. The severity of symptoms can vary greatly within families and, obviously, persons with CMT can live highly productive and satisfying lives. Sorting through these many issues can be difficult and stressful. Families considering the option of prenatal diagnosis should be provided with detailed genetic counselling. Additional Reading: The entire test offered by Athena is called the CMT1 Evaluation Profile and I'll give you some of the information the way Athena has written it. "Distinguishing between CMT1A and CMTX based on clinical and family history or nerve conduction velocities (NCV) results alone is often extremely difficult. Complicating the clinical diagnosis further is the high rate of affected female carriers of the CMTX mutations, thus the CMTX family pedigrees often do not demonstrate a X-linked transmission pattern (i.e., no male-to-male transmission of the disease). CMTX should be considered in all families without male-to-male transmission of the disease or when CMT1A has not already been molecularly diagnosed. The CMT1 Evaluation Profile is particularly valuable for differentiating between these most common types of CMT1. "If a CMT1A duplication is detected, a report is generated and the test is billed at $425. If the test is negative, Athena will perform the CMTX analysis and the complete profile will cost $770 U.S." All of this doesn't mean you can't fall through the cracks. Researchers are still finding other types of CMT on other genes. While the CMT1A and CMTX tests will provide information about the most common causes of CMT, negative CMT1A or CMTX tests do not rule out the possibility that you may have another type of CMT. The best candidates for the CMT1 Profile analysis are: 1) people who have chronic idiopathic demyelinating peripheral neuropathy, regardless of family history. 2) people with slow progressive atrophy of the distal muscles detectable as early as the first decade but often so mild as to be medically insignificant by the patient until early adulthood. Ninety-seven per cent of the people show clinical symptoms by age 27. 3) people with severely slowed motor nerve conduction velocity (NCV) of less than 41 m/sec. Reduced NCV may be noted several years before clinical symptoms can be detected. Typically, people with CMTX have: distal muscle atrophy and weakness including loss of balance (76% of patients), gait disturbance (73%), foot deformity (66%), frequent muscle cramps (62%), decreased exercise tolerance (60%), and reduced use and deformity of hands (59%). Also, sensory loss including absent or decreased reflexes (85%), cold hands and/or feet (67%) and numbness of hands and/or feet (41%). Not everyone has a family history of CMT and just 65% of those in the research had a history of it which says to me that many of the people who tell me they have no history, so it can't be CMT, might benefit from these tests. To date, there have been some 25 individual mutations identified which means if your test doesn't come up CMT1A or CMTX positive you could have another type of CMT that a test hasn't been developed for or a new type altogether. If you want to find out more, ask your doctor to call Athena and ask
for specific information such as how many tubes of blood are required
and what size, etc., or you can call yourself but a doctor has to draw
the blood for you and ensure it is shipped correctly.
|