While browsing through some of the research studies you may see terms or abbreviations that need a little more explanation. Below is a glossary to explain the meaning of some of the more common ones you will see.
Concordant: In a research study for twins, this would mean that both twins have that specific condition or disease that is being studied. For example, twins who are "concordant" for autism means that they are both autistic.
Discordant: In a research study for twins, this would mean that only one twin has that specific condition or disease that is being studied. For example, twins who are "discordant" for diabetes means that only one of the twins is diabetic.
Dizygotic or DZ: This is the scientific term for fraternal twins. Twins develop from two eggs (di=two, zygote=egg) that are fertilized separately by two different sperm Dizygotic, or fraternal, twins may be the same sex or opposite and may appear similar or look completely different.
Monozygotic or MZ: This is the scientific term for identical twins. Twins develop from one fertilized egg (mono=one, zygote=egg). This egg divides into two individuals who will share all of their genes in common. These twins are genetic clones of each other. They will therefore always be the same sex and have identical features, eye and hair color.
Source: Twins to Quints: The Complete Manual for Parents of Multiple Birth Children, Edited by Rebecca L. Moskwinski, M.D., ( 2002, Harpeth House Publishing)
Special thanks to J. Susan Griffith, M.D.