Cell structure, photo adapted from National Library of Medicine

Cell and Nucleus

The human body is made up of billions of cells, each with a nucleus in the center. The nucleus is like a “central office” for the cell, where the most important instructions come from for

  • How the cell will operate
  • What it will manufacture
  • How it will communicate with other cells

Most of a cell’s genetic material is stored in the nucleus.

cell in blue and nucleus in orange
cell (blue), nucleus (orange)

Deoxyribonucleic Acid (DNA) and Chromosomes

DNA double helix
DNA double helix
  • In a cell, the “instructions” come in the form of DNA.
  • DNA stands for deoxyribonucleic acid.
  • DNA is present in almost every human cell. It provides the blueprint or recipe for how our bodies grow, develop, and function.
  • DNA is a double helix (imagine a twisted ladder) that is made of two sugar and phosphate backbones and four different nitrogenous bases: adenine, thymine, guanine, and cytosine (A, T, G, and C).
  • DNA is packaged onto proteins called histones to form chromosomes.
  • Humans have 23 pairs of chromosomes, including the X and Y chromosomes. X and Y are the sex chromosomes that determine whether someone is male (XY) or female (XX).
  • The other 22 chromosome pairs are called the autosomes.

Genes

Each chromosome contains thousands of genes. A gene is a portion of DNA that codes for a protein.

  • Each gene is made up of billions of letters, which our body reads in three-letter units called codons.
  • Each three-letter codon determines a specific amino acid.
  • The amino acids are strung together to make proteins, such as hormones, enzymes, and antibodies.
  • The many genes that provide the instructions for the proteins in our bodies determine a wide range of features, including outwardly appearing physical traits such as height, eye color and hair color, to inner functioning, such as how each organ system works.
  • There are over 20,000 genes in the human genome! We are only beginning to understand how many of them might work.

Although genes and chromosomes are mostly similar from person to person, there is variation among people. Most of the time, this variation does not impact health or development. Genetic variation explains some of the wonderful differences that we see among humans.

  • Some variation in genes may not change amino acids or proteins.
  • Sometimes, however, changes in chromosomes or genes, may lead to developmental or medical issues such as epilepsy.

Gene Sequencing and the Human Genome

Gene sequencing determines the order of the four building blocks of DNA, the bases: A, G, T and C. The sequence tells scientists what genetic information is carried in parts of the DNA. Gene sequencing can bring to light changes (genetic variant) in a gene that may cause disease.

Knowledge about the human genome is in the early stages. The genome was fully sequenced for the first time in the year2000. It was not until a technology called next generation sequencing (NGS) became widely available, about a decade later, that rapid identification of “epilepsy genes” became a possibility.

DNA, Photo credit NIH.gov
Credit: NIH.gov

 

Over the past decade we have learned there are hundreds if not thousands of genes that play a role in epilepsy. Sometimes, a single change in a gene may be enough to cause epilepsy or an epilepsy syndrome. In other cases, it may be that gene changes increase the likelihood of epilepsy occurring in an individual, but perhaps an environmental factor is also required.

  • Genetic testing is now widely available for both children and adults with epilepsy.
  • A genetic diagnosis may provide valuable information about prognosis and treatment.
  • The field of epilepsy genetics is relatively new, and there is still much to learn.
  • There are ongoing research efforts to learn more about genetic changes that lead to epilepsy.
  • This knowledge will help to bring new and better treatments for individuals living with epilepsy.
Authored By: 
Sonal Mahida MGC, CGC
Authored Date: 
12/2019
Reviewed By: 
Annapurna Poduri MD, MPH
Beth Rosen Sheidley MS, CGC
Elaine Kiriakopoulos MD, MSc
Elaine Wirrell MD
Epilepsy Foundation Digital Strategies & Engagement
on: 
Thursday, April 23, 2020