Each year, many children born in the United States inherit an abnormal gene that will cause them to become ill. In order to find the best diagnostic and treatment options, affected individuals and their families need to understand the basics of the underlying genetics of these diseases.
Every person comes with a blueprint, known as the genome, which is contained inside each cell of the body in the form of deoxyribonucleic acid, or DNA. DNA tells each cell what to do and when to play its part. Within cells, DNA is organized into structures called chromosomes. Humans typically have 23 pairs of chromosomes for a total of 46 chromosomes—one set of 23 coming from the father and the other set from the mother. The diagram below shows how the coding for genetic diseases moves from parents to their offspring.
Chromosomes are made up of subunits called genes. A gene is the basic and functional unit of heredity. It provides the necessary instructions for a cell, telling it which specific proteins to produce. These proteins play many roles in the body and can affect physical characteristics, such as hair and eye color, as well as lead to certain genetic diseases.
Genes are made up of introns and exons. Exons are the parts of the gene that are most important for creating proteins. And the human exome is all of the exons in all of the genes, which account for less than 2 percent of an entire genome. Research has often focused on this 2 percent of the genome because it is more feasible to study and easier to compare data against existing research. But there is still a lot we do not understand about the exome.
This genetic information is encoded in genes using a four letter alphabet made up of the letters A, T, C, and G. The letters stand for the molecules adenine, thymine, cytosine, and guanine. These molecules form complimentary base pairs that make-up each of the 3 billion rungs of the twisted ladder that is DNA. When there are mistakes in the sequence of letters, called mutations, this can affect the production of the specific protein that the gene normally encodes. These mutations are either passed down from a parent to a child, or occur randomly in the egg or sperm.
Sometimes, mutations can be beneficial. One example is a mutation in the CCR5 gene. Normally this gene encodes a protein which makes white blood cells susceptible to the HIV viral infection. However, a specific mutation of the CCR5 gene—one that rarely occurs in the population—will give a person partial or complete protection against most forms of HIV. Although mutations can occasionally be beneficial, more often they can cause disease if the error happens in parts of genes that are important for regular body functions.
To learn more about genetics, inheritance, DNA, or genes, the Genetics Home Reference has a handbook dedicated to this subject. Additional educational information on rare diseases, genomics, and case studies can be found in the Diagnosing Rare Diseases e-book.
Genetics is complex. It can seem too abstract for some younger children to understand. But parents who want to share this information with their children may consider using GeneEd Web. GeneEd Web may seem more accessible to younger viewers because it introduces genetic topics, such as cell biology, DNA, genes, and chromosomes, with animation, games, videos, interactive tutorials, and experiment ideas.