An inherited condition is caused in whole or in part by a change (variant) in the DNA. Inherited conditions can be caused by a variant in one gene (monogenic disorder), by variants in multiple genes (multifactorial inheritance disorder), by a combination of genetic and environmental factors, or by damage to chromosomes (changes in the number or structure of entire chromosomes, the structures that carry genes). Genetic disorders are grouped into three categories: Monogenetic disorders are caused by a variant in a single gene. The variant may be present on one or both chromosomes (one chromosome inherited from each parent). Examples of monogenic disorders are: cystic fibrosis, Huntington’s disease and sickle cell disease. Multifactorial disorders are caused by a combination of variations in genes, often acting together with environmental factors. Behaviors are also multifactorial, involving multiple genes that are affected by a variety of other factors. Examples of multifactorial disorders are: Alzheimer’s disease and congenital heart disease. Chromosome disorders are caused by an excess or deficiency of the genes that are located on chromosomes. An example of a chromosome disorder is Down syndrome. Do you believe you or someone in your family can have or be at risk for a genetic condition? A Certified Genetic Counselor can offer professional guidance. Use our directory to find a CGC in your area.