Most diseases are multifactorial, and single-gene disorders are rare.
Environmental risk factors include exposure to toxins, poor nutrition, and trauma, in addition to others. There are strong genetic influences on psychiatric illness. Family studies investigate first-degree relatives.

Global developmental delay describes a child under the age of five who seems to be falling behind developmentally, but the practitioner cannot reliably assess the degree of impairment.
Borderline intellectual functioning describes a person nominally ranked in the IQ rank of 71 to 84 who does not have the coping problems associated with an intellectual disability.
Autism spectrum disorder forms in early childhood and results in impaired social interactions and communication. These patients usually demonstrate stereotyped behaviors and interests.
Unspecified intellectual disability is a term used when a child is five years old or older and cannot be reliably assessed due to a physical or mental impairment.

Around 25% of those diagnosed with a mood disorder experience manic or hypomanic episodes. Almost all patients who experience a manic or hypomanic episode also experience periods of depression. The severity and duration of the highs and lows differentiate the types of bipolar disorder:
* Bipolar I disorder: These patients experience at least one manic episode and may or may not experience a major depressive episode.
* Bipolar II disorder: These patients experience at least one hypomanic episode and at least one major depressive episode.
* Cyclothymic disorder: These patients experience mood swings, but they are not severe enough to be called major depressive episodes or manic episodes.
Schizoaffective disorder is a psychotic disorder characterized by patients experiencing symptoms of schizophrenia along with either depression or mania.

Healthcare system describes the organizational and institutional structures through which an economy makes choices regarding the production, consumption, and distribution of medical services.
Health production function is a mathematical expression that shows the relationship between an individual's health and several other variables, including the amount of healthcare consumed.
A health alliance is a public agency that uses its bargaining power to negotiate competitive prices for health insurance from the private insurance market.
Health economics is related to the value, effectiveness, and efficiency of care received and does not describe the organizational and institutional structures by which economic decisions are made.

Cyclothymic disorder is a mental disorder that involves numerous periods of depressive symptoms and hypomanic symptoms. However, these symptoms are not sufficient to be diagnosed as a major depressive episode or a hypomanic episode.
Medical conditions associated with cyclothymic disorder include, but are not limited to, hypercortisolism, multiple sclerosis, stroke, traumatic brain injury, or systemic lupus erythematosus.
Cerebral palsy, muscular dystrophy, and amyotrophic lateral sclerosis are not commonly associated with mood swings or emotional ability.