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Endophenotypes

In 1973, professor of psychology Irving Gottesman and his colleague, James Shields, introduced the term endophenotype into human psychiatric genetic research as a result of their groundbreaking research studying schizophrenia in twins and families. Their work centered on identifying behavioral characteristics that occurred as a result of genetics. Endo refers to the concept of “within” or “internal.” Thus, endophenotype embodies a measurable, behavioral characteristic clearly associated with a genetic condition. This entry discusses the different natures of enophenotypes, as well as past and current research concerning them.

Genotypes and Phenotypes

A genome is akin to an individual’s set of instructions or personal programming code, which determines at a cellular level exactly who that individual is. An early distinction in genetic research was the difference between genotype and phenotype. Genotype refers to heritable genetic identity and represents a unique genome identified by individual genome sequencing, that is, an analysis of a person’s entire genetic code. Genotype can also refer to a certain gene or set of genes that can identify particular mutations linked to disease or a disorder (e.g., diabetes). Molecular biology techniques measure genotypes and can help predict the probability of a disease. These techniques include polymerase chain reaction (PCR), a widely used test tube procedure that can create multiple copies of select DNA and determine DNA sequencing.

Phenotype describes tangible physical characteristics such as height and eye color, overall health, and possibly behavior or general disposition. Phenotypes may or may not be a result of genotype, as phenotypes can be influenced by environment and life experiences. For example, the development of a phobia may occur after a traumatic or significant life experience such as an encounter with a very unpleasant animal. In some instances, the term intermediate phenotype is referred to as an endophenotype.

Origins of Human Genetic Research

Human genetics is a relatively young field of study. Biologist William Bateson first coined the term genetics in 1902, DNA was discovered in 1953, and the sequencing of the human genome was completed in 2003. Research continues to explore the many variables of human genetics and pave the way for new insight into the human makeup, both as groups of people and as individuals.

As in much of biological and psychological research, efforts to organize and perhaps classify genetic differences began in animal research. The initial focus of such research is often molecular, with intent on isolation and identification. Later, the focus shifts to more complex organisms, such as animals, followed by humans. Following more than 30 years of research along this line, in 2003, Gottesman and Gould reviewed the concept of endophenotype. They indicated that the nature of endophenotypes could be neurophysiological, neuroanatomical, biochemical, endocrinological, cognitive, and neuropsychological.

Types of Enophenotypes

Neurophysiological endophenotypes apply to the function of the nervous system within the body, whereas neuroanatomical endophenotypes focus on the structure of the nervous system. Biochemical endophenotypes involve chemical processes linked to and within living organisms, whereas endocrinological endophenotypes deal with the endocrine system, endocrine diseases, and hormones. Cognitive endophenotypes relate to or involve mindful intellectual activities such as thinking, understanding, learning, and remembering. Neuropsychological endophenotypes help explain neurological sources of individual differences and assist in identifying brain-based disorders in emotional expression, personality, self-awareness, attention, memory, and cognition.

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