Twin biology: Chorionicity of the placenta


  1. MZ twins may well have more difficulty in individuating, and require special social and educational considerations.
  2. There are high concordance rates in MZ twins for many chronic disorders with a genetic background, e.g., allergies, asthma, heart disease, Alzheimer's, schizophrenia, diabetes, neuroses, cancer. These disorders may not actually happen simultaneously, but they can be anticipated in the second twin if they occur in the first twin.
  3. MZ twins can serve as rejection-free organ transplant donors for their co-twins.
  4. Medical research needs MZ and DZ twins to sort out the relative importance of environmental and genetic factors in the development of normal people as well as their disorders and diseases. Many twins are eager to participate in these studies for the good of all as well as to learn more about twinning. Not everybody wants to participate, but the studies are non-harmful and non-interventional. They contribute greatly to the cause of disease prevention.

Zygosity can be determined as follows:

  1. Monoehorionic (MC) twins are all monozygotic (MZ).
  2. Unlike-sexed twins are dichodonic (DC) and dizygotic (DZ).
  3. Not all dichorionic (DC) twins are dizygotic (DZ).
  4. Like-sexed dichorionic (DC) twins need testing for zygosity.

The zygosity test of choice is DNA fingerprinting, a non-invasive procedure which currently costs about $100. This is not at present considered a standard part of the care of twins. I believe that it should be and that parents and twins and others should lobby for it.

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