An Introduction to Insensitivity
In this section, we will begin by describing some of the basic biological terms that will help you to understand the information regarding the disorders associated with insensitivity to pain! The terms you will need to feel confident with to understand the descriptions of the biological causes of these disorders are chromosomes, genes, genetic mutations and voltage-gated ion channels. After we discuss the vocabulary, we will discuss two known disorders characterized by the insensitivity to pain, Familial Dysautonomia and Congenital Insensitivity to Pain, and their biological causes.
Chromosomes are tightly woven strands of DNA that are found in the cells of organisms. We, as humans, have 46 chromosomes (arranged as 23 pairs), 23 of which come from each parent. Each pair of chromosomes has one chromosome from one parent, and one from the other. Each pair of chromosomes contains hereditary information from each parent in the form of genes.
As you can see in these images, each pair of chromosomes
consists of one chromosome from each parent. The first 22 pairs are what
are known as “autosomal” chromosomes, meaning they are chromosomes that do not
code for the organism’s gender. The last pair is of sex chromosomes which
determine the gender of 
the child.
A gene is a collection of hereditary information that is located on each chromosome and that determines a particular characteristic of an organism. The genes that are reflected in the characteristics of the organism are determined by which genes are recessive and which are dominant. Each pair of chromosomes has complementary genes that code for a specific characteristic. Each complementary gene is either recessive or dominant. This means, each parent will give one of the complementary genes to the child, randomly determined to be recessive or dominant. If both parents give a dominant gene, the dominant gene’s characteristic will be apparent in the offspring. If either one of the parents, but not both, give the offspring the recessive form of the gene, the offspring will display the characteristic of the dominant gene. However, if both of the parents provide the offspring with the recessive forms of the gene, the offspring will display the characteristic of the recessive gene. Here is a visual to help you understand:
In this image, the two characters at the top represent the parents. R represents the dominant gene, and r represents the recessive gene. Therefore, if both parents contain the gene pair of one dominant gene and one recessive gene, they are able to pass on any combination of the gene to their offspring. This is shown by the figures at the bottom. As you can see, the blue figure has the genetic coding of both dominant genes from the parents. Therefore, the blue figure will display the dominant characteristic. Two of the figures (the purple ones) are represented as having both a dominant gene and a recessive gene. The red figure, containing both the recessive genes, will portray the recessive characteristic. As can be seen from the image, the chance of receiving both of the recessive genes from parents containing both dominant and recessive genes is only a one-in-four chance.
This is an image of a chromosome, with each band on the
chromosome representing a different gene.
Genetic mutations are caused when their particular DNA sequence are changed. These mutations can result in the creation of a new characteristic or trait that is not present in either parent. The offspring with the mutation may then pass on the mutated gene to another offspring, in the form of a recessive gene. If two of the parents happen to have the mutated gene in the form of their recessive gene, then the child has a 25% chance of receiving both of the recessive genes, which would cause the mutated characteristic to be evident in the offspring.
Genetic mutations can change the DNA sequence on a specific section of a chromosome. The effects of the genetic mutation are based on the area of the chromosome and the specific chromosome that the mutation is on.
Voltage-Gated Sodium Ion Channel
Ion channels are channels set in a cell’s membrane, or a thin layer that encloses the insides of a cell, that selectively allow ions in and out.
Sodium ion channels, the green objects located on the cell membrane, are ion channels that specifically allow only sodium ions, represented by the yellow dots, through the membrane. Voltage-gated ion channels are ion channels that are activated to open or close because of an electrical signal generated by the nervous system. Therefore, a voltage-gated sodium ion channel is a sodium ion channel that is activated by an electrical signal. The voltage-gated sodium ion channel is strongly expressed in neurons that respond to pain signals. These neurons receive their information from the sodium ions flowing into the cells through these channels, which then activate the neurons to send the pain information towards the brain.
Picture References: (from top to bottom)
http://alphabeticaprime.files.wordpress.com/2007/09/chromosomes_23.jpg
http://www.sciencemuseum.org.uk/on-line/genes/images/1-3-4-6-0-0-0-0-0-0-0.jpg
http://biology.unm.edu/ccouncil/Biology_124/Images/chromosome.gif
