The Colorado Longitudinal Twin Study (LTS) is one of the landmark twin studies conducted in the United States today. Based at the University of Colorado’s Institute for Behavioral Genetics (IBG), it’s origins lie with the Early Childhood Transitions Network. In 1982 this community of research professionals conceived the idea of a longitudinal twin study in order to study the processes influencing developmental transitions from infancy to early childhood. After several years of planning, IBG researchers Robert Plomin and John Defries initiated the MALTS (the study was originally called the MacArthur Longitudinal Twin Study after the John D. and Catherine D. MacArthur Foundation, which funded the project from 1982 – 1994). Now simply referred to as the LTS, the Colorado Longitudinal Twin Study continues to research life transitions as twins who were once infants approach adulthood. Some areas of focus include the genetic and environmental contributions to cognition, empathy, temperament, and the onset of drug and alcohol abuse. The current investigators on the project are DeFries, Plomin, John Hewitt, Robin Corley, Naomi Friedman, Akira Miyake, Soo Rhee, Sally Wadsworth and Susan Young.

Recruitment for the LTS began in 1986. Twins and their parents were located through birth records provided by the Division of Vital Statistics of the Colorado Department of Health. Families who met certain criteria (twins with normal birth weights, gestation periods, and a residence located within 2 hours of Boulder, Colorado) were contacted and asked to participate. Eventually, 408 families agreed. Of the 408, 56% had already participated in the Twin Infant Project (TIP) conducted at the University of Colorado. The remaining twin pairs and their families were recruited from 1986 through the fall of 1990.

The initial study called for home and lab visits at ages 14 months, 20 months, 24 months and ending at 36 months. The twins and their mother were visited by two female examiners at their homes, and approximately two weeks later the mother would bring her children to the laboratory at the Institute for Behavioral Genetics. A wide variety of measures were conducted during these visits with both the children and their mother. (click on any age to view the specific assessments given at that time). Due to the success of the project and the excitement regarding the wealth of data, the LTS was extended to continue until the twins were 7 years old. At ages 4 and 5, examiners visited the twins at home, at age 6 an interview was completed with the parents, and at age 7 the twins participated in a home visit as well as a lab visit conducted after the twins completed first grade. Again the success of the study, particularly the low attrition rate and rich data sets, led to several renewal grants which continue to this day. At age 8 a parent interview is conducted, and at 9, 10 and 11 the twins are given various batteries over the phone. At age 12 they come back to IBG for a full day in the lab. At 13, 14, and 15 more telephone interviews are conducted. At 16 a lab visit is scheduled, and another is completed at age 17. Currently, the oldest twins participating in the LTS are 17 years old.

Throughout the Colorado Longitudinal Twin Study much has been learned about the transitions children make from infancy to early childhood to late childhood and into adolescence. Important developmental milestones mark all of these transitions, and both genetics and environment play a role in the success with which these milestones are met. Currently, researchers with the LTS are pursuing renewal funds in order to study the next major transition, that from adolescence into adulthood.