About Genetic Services

Ancillary Services

In addition to diagnosing genetic disorders and identifying disease susceptibilities, DNA technology can also be used to determine relationships between family members (parentage and zygosity testing), to identify genes that do not directly cause disease but may sometimes be associated with health problems (genotyping), and to store DNA for possible testing in the future (DNA banking).

Parentage Testing (Paternity or Maternity Testing)

In parentage testing, DNA sequences from a particular child and a particular adult are compared to estimate the probability that the individuals are related. Most indications for parentage testing are social, but establishing parentage is occasionally necessary for the correct interpretation of family DNA studies.

Points to consider:

• A particular individual can be reliably excluded as a biological parent using DNA testing, but cannot be absolutely confirmed.
• Laboratories differ in the number of DNA sequences compared, so statistical reliability varies among laboratories.
• Parentage testing can be expensive and is not generally covered by medical insurance.
• Some laboratories offer parentage testing prenatally.
• If testing is to be done for legal purposes, special arrangements must be made to ensure chain-of-custody of the sample.

Zygosity Testing

Zygosity testing compares DNA sequences to assess whether individuals born from a multiple gestation (twins, triplets, etc.) are monozygotic (identical) or dizygotic (fraternal). The primary medical indications for zygosity testing are to identify a donor for organ transplant (monozygotic siblings are the best donors) and to estimate disease susceptibility risks (if one monozygotic sibling is affected, the other(s) is/are at high risk).

Points to consider:

• If the twins (or multiples) are in separate chorionic sacs, zygosity cannot be determined without testing. If twins (or multiples) are in the same chorionic sac, they are monozygotic even if their appearance is different.
• If genetic testing for a disease is being considered, zygosity of twins or multiples becomes an issue, because the genetic diagnosis of one may apply to the other(s) as well (Clinical Example).
• Laboratories differ in the number of DNA sequences compared, so statistical reliability varies among laboratories.

Genotyping

Many genes have variations that do not directly cause disease but may be associated with health problems. Genotyping determines which of these variations are present in an individual. Knowing which specific forms of a particular gene are present can sometimes be important for medical management (Clinical Example).

DNA Banking

DNA banking involves extracting DNA from cells and freezing or refrigerating it for future testing. DNA can be stored for years. DNA banking is offered to terminally ill patients with a known or suspected genetic disorder, individuals with a genetic disorder for which no testing is yet available, or people who do not presently wish to pursue available testing but would like to reserve the option for the future.

Points to consider:

• The cost of DNA banking is often not covered by insurance; however, the cost is small.
• Laboratories offering this service may charge a one-time fee for DNA banking for an indefinite period, or charge an initial set-up fee plus periodic payments to maintain the sample.
• It is important to understand the laboratory's DNA Banking policies and procedures (see sample consent form: CompGene) for sample storage and release.
• It is important for family members to agree, at the time of DNA banking, who has access to the sample for testing purposes after the donor's death (Clinical Example).
• Careful documentation and communication about the banked DNA sample is necessary so that family members know the sample exists.
  
  

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(Revised 3-19-04)