Although a person may appear physically fit and trim on the outside, she may be dealing with serious health issues on the inside. Monogenic and multifactorial inheritance disorders such as mental illness, alcoholism, diabetes and heart disease may not show any obvious physical signs and symptoms. Furthermore, some people may eat an unhealthy diet or enjoy unhealthy habits and still look fit and trim.
Monogenic Disorders
According to the National Human Genome Research Institute, monogenic disorders are a condition where one or both chromosomes are mutated. There are more than 10,000 diseases that fall under this category. Common monogenic disorders include cystic fibrosis, polycystic kidney disease, sickle cell anemia, hemophilia, diabetes and heart disease. Many of these illnesses show no obvious signs or symptoms that would lead you to believe that the affected person is unhealthy. Many live active, full lives despite their health conditions.
Multifactorial Inheritance Disorders
Diseases and health conditions that fall under the category of multifactorial inheritance disorders involve genes as well as environmental factors. Alcoholism, for example, may be caused by an inheritance of slightly mutated genes from one or both parents as well as lifestyle choices and environmental factors such as life at home and a family history of alcoholism. Multifactorial inheritance disorders may include diabetes, heart disease and hypertension as well as behavioral disorders such as obesity, Alzheimer's, autism, schizophrenia, bipolar disorder and other mental illnesses.
Chromosomal Abnormalities
Although some chromosomal abnormalities such as Down and Turner syndromes, may show outward signs and symptoms, other chromosomal abnormalities do not. Examples include Triple X, Klinefelter syndrome and XYY. Boys who are born with an extra Y chromosome and girls who are born with an extra X chromosome may be taller than their peers and may experience learning or behavior problems as children, but show no other sign or symptom of their condition. Men affected with Klinefelter syndrome may have lower amounts of testosterone, which may make them infertile, but they show no other obvious sign of their condition.
Other Considerations
Though a person appears physically fit on the outside, he may have a serious unknown health condition, such as a blood clot or cancer, or his internal organs may be surrounded by visceral fat. Internal visceral fat is just as dangerous as someone who appears to be overweight or obese. Physically fit people may also have unhealthy habits, such as smoking or using illicit drugs, or may participate in risky behaviors such as unprotected sex and intravenous drug use.
References
- National Human Genome Research Institute: Frequently Asked Questions about Genetic Disorders
- World Health Organization: Genes and Human Disease
- Encyclopedia Britannica: Diseases Caused by Mutlifactorial Inheritance
- March of Dimes: Chromosomal Abnormalities
- MSNBC; Thin People Can Be Fat on the Inside; Associated Press; May 2007
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