What are Genes?

Genes are the basic instructions that our bodies use to function, and we inherit them from our parents. Imagine genes as recipes that tell our bodies how to make important molecules like proteins.

Our bodies are made up of tiny building blocks called cells. Inside each cell is a nucleus, which acts like the brain of the cell and tells it what to do. The nucleus holds chromosomes, which are thread-like, X-shaped structures packed with DNA. Humans have 46 chromosomes, or 23 pairs, which contain the DNA that makes each of us unique. Specific sequences of DNA are classified as genes.

DNA forms a long, twisting molecule shaped like a ladder, called a double helix. Four chemical bases make up DNA, and they are referred to as the letters A, T, C, and G. These letters form a code that guides cells on how to work. Although most of our DNA is the same across all people, minor differences in certain genes, called alleles, make us unique.

Alleles are different versions of a gene, like you and a friend following the same recipe but adding your own twist, which leads to unique final results. These variations are why we have diverse hair and eye colors. Ultimately, each chromosome is made up of thousands of genes, which are specific ordered sections of DNA. These genes have small differences across thousands of base pairs that make you unique and different from everyone else.

Proteins do most of the heavy lifting in the body—building tissues, sending signals, and even fighting infections. Not all genes directly make proteins. Some simply help control other genes. Genes can also have “errors” or changes, which are known as gene mutations. Think of these as a typo in a recipe or a missing ingredient. While some mutations don’t affect us, others can drastically change how cells work and cause health issues. Mutations can happen for various reasons, such as exposure to certain chemicals, radiation, or simply by chance. In certain cases, like HSAN1E, mutations interfere with nerve function, which lead to symptoms specific to that condition. The gene impacted in HSAN1E is the DNMT1 gene. It provides instructions for making an enzyme called DNA methyltransferase 1. This enzyme may help regulate nerve cell (neuron) maturation and specialization, as well as impact the ability of neurons to move and connect with each other. It plays an active role in the adult nervous system. At least 10 DNMT1 gene mutations have been identified in people with HSAN1E and at least 4 DNMT1 gene mutations have been identified in people with ADCADN. Most mutations that cause HSAN1E and ADCADN occur in two parts of the gene called exon 20 and exon 21.