Non-communicable diseases (NCDs) are disease processes that are not contagious or transferable from one human to another. Random genetic abnormalities, heredity, lifestyle or environment can cause non-communicable diseases, such as cancer, diabetes, asthma, hypertension and osteoporosis.

Dopamine is a natural chemical substance that is produced from the amino acid tyrosine by a mid-brain structure called the substantia nigra. As a neurotransmitter, dopamine transmits chemical signals from the dopamine-containing neurons to target cells that contain dopamine receptors.

Personality characteristics have been a common focal point in psychological research studies through the years, and there has always been discussion as to how many family influences play a role in personality development.

Genetic diseases result from mutations or abnormalities on chromosomes or genes. Some ethnic groups are at higher risk for some genetic diseases than others, but the diseases can occur in any group, according to the Genetic Disease Foundation.

Narcissism or narcissistic personality disorder is a diagnosis under the classification of personality disorders. Narcissistic rage occurs when the person with narcissism perceives he's being attacked by another.

Infrequent occurrences of eye twitching are normal, but eye twitching can also be a continuous or a frequent phenomenon, and can be a symptom of a neurological disorder, reports the American Psychiatric Association.

A parasite is an organism that depends on a living host for its survival. Usually, the parasite derives all the benefit from the infection, to the detriment of the host. Parasitology is the study of this relationship between parasite and host.