Eye Color as a Potential Clinical Phenotype of ASD

Background:

Recent epidemiological studies have shown increased interest in eye color variation among medically relevant populations. Eye color has proven relevant to risk of macular degeneration, glaucoma, and melanoma; and is significant to the phenotype of multiple genetic disorders, including Waardenburg, Angelman and Prader-Willi Syndromes. However, little is known about eye color and Autism Spectrum Disorder (ASD). The gene for eye color, Herc2, is located on chromosome 15, an area of interest for ASD. Additionally, melanin, the pigment responsible for eye color, may have a role in the ascending reticular activation system regarding arousal and ASD. The purpose of this study is to explore the relationship between eye color and ASD, regarding its genetics and physiology, its relationship to the development of ASD and its use in defining a clinical phenotype for ASD.

A 1994 study conducted on individuals born between 1936 and 1951 calculated the rate of blue eye color in the United States for non-Hispanic Caucasians as 33.8%. Due to immigration and changes in culture, the proportion of blue eyed individuals in the United States is decreasing, and may be lower for this study’s population of subjects.

Objectives:

To observe eye color in a population of children with ASD in relation to dysmorphic features, cognition and the core deficits of ASD (impaired social interaction and communication, and restricted and repetitive behaviors). Demographic variables, such as ethnicity and gender will also be examined.

Methods:

Child eye color was observed during clinic visits from the PA-SEED (Study to Explore Early Development) population, and photographic records were made. Characterization was made by a clinician, both in person and photographically, and was validated by a second clinician. Basic eye color choices were used, including blue, green, hazel, brown and black.

Results:

Of the current sample of 34 children, 23 scored positive on one of the gold standard ASD diagnostic instruments (ADI-R or ADOS). 16 of these children rated their ethnicities as non-Hispanic Caucasian. The distribution of eye color for these 16 children was as follows: 8 blue eyed, 2 green eyed and 6 brown eyed. The male to female ratio was 14:2. Other syndromes and developmental disorders were also present in this population. Additional subjects will be recruited, and their results added to the sample. A larger sample is needed to report eye color statistics in non-ASD research subjects. Correlations regarding dysmorphic features and results of cognitive instruments will be reported when a larger sample is collected.

Conclusions:

50% of the non-Hispanic Caucasian children who scored on the ADOS or ADI-R had blue eyes, while 12.5% had green eyes and 37.5% had brown eyes. The increased percentage of children with blue eyes in the selected study population, compared to the general population distribution, deserves further exploration. Further investigation into the genetics and physiology of melanin production, its role in the brain and iris, and the timeline of its development may allow the use of eye color as one component of a clinical phenotype for a subset of the ASD population.