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Frequently Asked Questions
- What is the detection rate for the Duchenne/Becker Muscular Dystrophy carrier test?
This assay detects deletions, duplications and rearrangements in the dystrophin gene that account for 60 - 70% of the mutations found in carriers. If a woman is the relative of an affected individual with a known mutation, please supply this information with the blood sample as it will greatly increase the laboratory's ability to calculate residual carrier risk following testing.
- A boy tests positive for a Duchenne muscular dystrophy (DMD) deletion mutation. His mother tests negative for the DMD deletion mutation found in her son. Why does his mother still have a 15% carrier risk?
Given that the mother has no affected siblings, the possibility that she is germline mosaic cannot be ruled out (mutation is carried in a proportion of her gametes but not in her somatic cells, e.g., blood cells) for a DMD mutation.
- Why pursue DNA testing in addition to dystrophin analysis for DMD?
The identification of a mutation in the Dystrophin gene enables direct prenatal diagnosis for male fetuses and carrier testing for female relatives.
- If a symptomatic patient has a negative genetic test result, does it mean the patient is not affected with the tested disorder?
Possible explanations for an affected individual testing negative for a disorder include: - Genetic heterogeneity - disease may be caused by multiple genes which may not be included in the analysis. For example, a patient with a negative SOD1 sequence analysis may still be affected with Familial Amyotrophic Lateral Sclerosis (FALS) because she possesses a mutation in a different FALS-associated gene.
- Allelic heterogeneity - disease may be caused by several different mutations within the same gene, which may not be included in the assay. For example, in rare cases, Friedreich's Ataxia can be caused by the combination of a point mutation in one Frataxin gene and an expansion in the other gene; thus an affected individual may appear to be only a carrier of the disorder.
- When there is a family history of a genetic disorder, is it necessary to test an affected family member before testing presymptomatic family members?
Ideally, an affected family member should be tested first in order to confirm the diagnosis and the type of mutation. In the absence of this information, the significance of a negative test result is reduced.
The importance of identifying a mutation in an affected individual prior to presymptomatic testing in other family members is illustrated in the case of Early Onset Familial Alzheimer's Disease (EOFAD). At least three genes are known to be associated with EOFAD. Mutations in the Presenilin-1 gene are known to be associated with 50 - 60% of EOFAD cases. Without verification of a familial Presenilin-1 mutation, there are three possible explanations for a presymptomatic individual testing negative: one, the patient is negative for the familial mutation, two, the patient is negative for a mutation in an untested gene, three, the patient is positive for a mutation in an untested gene. Confirmation of a Presenilin-1 mutation in an affected family member would eliminate the latter two possibilities in this scenario.
- How can I inquire about the availability of prenatal diagnosis?
Always contact Athena's genetic counselor before the collection and shipping of prenatal samples.
Athena requires a maternal blood sample for maternal cell contamination studies as well as family history.
- How should testing for Charcot-Marie-Tooth Disease Type 1 (CMT1) be approached?
It can be difficult to distinguish between the subtypes of CMT Type 1 and the HMSNs. For this reason, Athena offers a series of panels that address a variety of clinical pictures (the individual tests may also be ordered separately).
Download the CMT Patient Booklet (PDF).
- Complete CMT Evaluation
- For patients with slowly progressive distal muscle atrophy, weakness, and abnormal NCV.
- Includes PMP22 duplication and deletion testing and sequence analysis of PMP22, Connexin32, MPZ, EGR2, NFL, Periaxin, GDAP1, LITAF/SIMPLE and MFN2.
- Partial CMT - Demyelinating Only
- For patients with slowly progressive distal muscle atrophy, weakness, and slowed NCV.
- Includes PMP22 duplication and deletion testing and sequence analysis of PMP22, Connexin32, MPZ, EGR2, GDAP1, PRX, and LITAF/SIMPLE.
- Partial CMT - Axonal Only
- For patients with slowly progressive distal muscle atrophy, weakness, and normal NCV.
- Includes sequence analysis of MPZ, Connexin32, NFL, GDAP1 and MFN2.
- Dominant CMT Evaluation:
- For patients with slowly progressive distal muscle atrophy, weakness, slowed NCV, and a clear dominant family history.
- Includes PMP22 duplication and deletion testing and sequence analysis of PMP22, Connexin32, MPZ, EGR2, NFL, LITAF/SIMPLE and MFN2.
- Complete HNPP Evaluation:
- For patients with transient, asymmetric, remitting motor neuropathy and slowed NCV.
- Includes PMP-22 duplication and deletion testing and sequence analysis of PMP22.
- Complete Dejerine-Sottas Neuropathy Evaluation:
- For children with delayed motor development, distal muscle weakness, and slowed NCV.
- Includes sequence analysis of PMP22, MPZ, EGR2 and Periaxin.
- Congenital Hypomyelination Evaluation:
- For infants with weakness, severe hypotonia, and slow motor development.
- Includes sequence analysis of MPZ and EGR2.
- Are there any cures for genetic diseases?
Although there are treatments for the symptoms of genetic disease, there are presently no cures. Research in the field of gene therapy may provide new avenues for the treatment and cure of genetic diseases.
- How can I learn more about presymptomatic testing for Huntington's disease?
Athena has developed a "Huntington's Disease Presymptomatic Testing Action Pack" which includes the following: - Reference information: Guidelines published by the Huntington's Disease Society of America, Inc. and the American Academy of Neurology; and an article from the American Journal of Human Genetics describing the psychological implications of presymptomatic Huntington's Disease testing
- Patient literature
- A clinician agreement for testing which is required prior to testing of a sample.
Please contact client services to obtain an information packet or to have an Action Pack shipped to you overnight.
- What do I do if I don't understand my test result?
Physicians and genetic counselors should feel free to contact Athena's genetic counselor to discuss the result of any of our assays.
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