You may have heard of the term ‘gene’ or ‘genetic’. This term refers to the way the body inherits information from each parent. When we are born we receive half our genetic information from one parent and the other half from the other parent. Unless they are identical twins, children from the same parents will have slightly different genetic information giving each of them their own unique character. The important genetic information is packaged in chromosomes. We usually have 46 chromosomes in each cell, and 23 come from each parent. Some conditions are due to a single abnormality in a chromosome. If a child inherits that abnormality from one parent they also have that susceptibility to developing disease. This sort of inheritance of a condition (called autosomal dominant) is not common but is important when it occurs: MODY is an example of this sort of inheritance. The mother of person A has the condition and passes it onto to A. In an autosomal dominant condition A has a 50:50 chance of receiving the gene from the parent with the condition (the mother) and therefore a 50:50 chance of having the condition themselves and therefore passing it on to the next generation.
Some conditions need the child to inherit the same abnormal gene from each parent before he or she develops the disease (autosomal recessive, they are a gene carrier). If the son or daughter receives the gene from just one parent they do not have the condition but may pass on the abnormal gene if they have a child themselves. An example of a condition that is inherited in this way is cystic fibrosis. In this case, neither parent shows the condition but they both carry the gene. Each child has a 50:50 chance of receiving the gene from each parent. This will give on average, one child with two unaffected genes, one child with both affected genes and two children who each have one affected gene and one unaffected gene. One in four of these children will have the condition and two will be carriers on average, but a family of four children may have no affected children, or more than one affected child, simply by chance.
Many conditions are multifactorial as many factors are important in developing the condition. Diabetes is thought to be a multifactorial condition. Genes may play a part, and it is thought that for most people with either Type 1 or Type 2 diabetes many different genes may be important, although environmental factors are equally or even more important.