Controlling for environmental differences, two teams in an international collaboration employed a twin study to determine the extent to which genes and/or environment influence musical pitch recognition ability. A twin study can discriminate the effects of environment from those of genes. The collaboration between scientists at the National Institute on Deafness and Other Communication Disorders and a team at the Twin Research and Genetic Epidemiology Unit, St. Thomas' Hospital in London employed an updated Distorted Tunes Test (DTT) and a standard Five Minute Hearing Test to (FMHT) used to help identify subjects with possible confounding hearing loss.
The DTT was developed in the 1940s, but was updated and validated for the current U.S. and British populations. To test the validity of the updated DTT, first, 50 unrelated males and 50 unrelated females were tested on the new DTT. The distribution scores on males and females did not differ. Test and re-test scores on the same individual were highly correlated, which confirmed that the updated DTT is reproducible in individuals.
The updated DTT was recorded on a compact disc and presented to all subjects in the same setting. Subjects were presented with 26 short popular melodies, ranging in length from 12 to 26 notes. Tunes were presented once, and after each presentation, subjects were asked to score whether the melody was correct or incorrect and whether they were familiar or unfamiliar with that melody.
A total of 284 female Caucasian twin pairs; 136 identical and 148 non-identical twins aged 18-74, participated in the study. The twins were part of an ongoing study of common complex diseases, were unaware of the specific hypothesis tested, and were not screened for IQ, musical training or musical experience.
Following the FMHT and the DTT, the teams subjected the data to genetic model fitting techniques using a structural equation modeling package. This was applied to determine estimates of the genetic and environmental factors. Model fitting allows separation of the observed phenotypic variance into additive or dominant genetic components and common and unique environment. The last also includes measurement error.
Heritability estimates the extent to which variation in a trait in a population can be explained by genetic variation.
Heritability for pitch recognition was estimated at 71-80%, depending upon how subjects were categorized. No dominant genetic effect nor significant effect of shared environment were detected. The heritability estimates observed for measures of deficit in pitch perception were very substantial and are high or higher than those for many complex traits in humans.
Dennis Drayna, lead author on the paper and a special expert, section on Genetics of Human Communication, Laboratory of Molecular Biology at NIDCD, notes "Since the FMHT serves as a rough estimate of peripheral hearing, its poor correlation with DTT suggest that musical pitch perception is largely independent of peripheral hearing. This would mean that variation in pitch perception originates in portions of the auditory system that are not dependent upon peripheral hearing, " adding, "the next important steps are finding the number of genes involved and the relative effects of those genes."
"Drs. Drayna (NIDCD) and Spector (St. Thomas') have demonstrated the importance of applying genetic approaches to biochemical or cellular mechanisms underlying neural function. Genetic modeling will yield substantial new understanding of the mechanisms applied to human communication research," said James F. Battey, Jr. M.D., Director of the NIDCD.
The Twin Research and Genetic Epidemiology Unit, St. Thomas' Hospital, uncovers the genetic basis of common diseases and traits associated with aging using twins. The unit has already made progress on the genetic basis of a number of diseases, including, osteoporosis, back pain, osteoarthritis, cataract, obesity, blood
clotting, hypertension and asthma.
NIDCD conducts and supports research and research training in the normal mechanisms and diseases and disorders of human communication. Within NIDCD's research efforts, scientists are using molecular genetics to understand both the normal and disease processes of human communication and the effects of inheritance and environment on those processes. NIDCD is one of the Institutes of the National Institutes of Health.
To arrange an interview with Dr. Drayna, please, contact the Office of Health Communication and Public Liaison at 301-496-7243.