Family aggregation, also known as familial aggregation, is the clustering of certain
traits, behaviours, or disorders within a given family. Family aggregation may arise because of
genetic or environmental similarities.
[Butcher, J., S. Mineka, and J. Hooley. Abnormal Psychology. 15. Boston: Pearson, 2010. Print.]
Schizophrenia
The data from the family aggregation studies have been extensively studied to determine the mode of inheritance of
schizophrenia
Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...
. Studies to date have shown that when numerous families are studied, simple modes of inheritance are not statistically supported. The majority of studies analyzing for the mode of inheritance have concluded that a multifactorial threshold mode is most likely.
Cardiovascular problems
The most consistent and dramatic evidence of family influences on
cardiovascular disease
Cardiovascular disease (CVD) is any disease involving the heart or blood vessels. CVDs constitute a class of diseases that includes: coronary artery diseases (e.g. angina, heart attack), heart failure, hypertensive heart disease, rheumati ...
(CVD) is family aggregation of physiological factors. In several studies the parent-child and sibling-sibling correlations of
blood pressure
Blood pressure (BP) is the pressure of Circulatory system, circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term ...
are approximately .24. Genetic determination of blood pressure is strong, but does not explain all of the variance.
Parkinson's disease
Familial
Parkinson's disease
Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...
(PD) exists but is infrequent. Early investigations failed to show substantial family aggregation for PD.
References
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Classical genetics