What are the genetic changes related to palmoplantar keratoderma with deafness ?
Palmoplantar keratoderma with deafness can be caused by mutations in the GJB2 or MT-TS1 genes.  The GJB2 gene provides instructions for making a protein called gap junction beta 2, more commonly known as connexin 26. Connexin 26 is a member of the connexin protein family. Connexin proteins form channels called gap junctions that permit the transport of nutrients, charged atoms (ions), and signaling molecules between neighboring cells that are in contact with each other. Gap junctions made with connexin 26 transport potassium ions and certain small molecules.  Connexin 26 is found in cells throughout the body, including the inner ear and the skin. In the inner ear, channels made from connexin 26 are found in a snail-shaped structure called the cochlea. These channels may help to maintain the proper level of potassium ions required for the conversion of sound waves to electrical nerve impulses. This conversion is essential for normal hearing. In addition, connexin 26 may be involved in the maturation of certain cells in the cochlea. Connexin 26 also plays a role in the growth, maturation, and stability of the outermost layer of skin (the epidermis).  The GJB2 gene mutations that cause palmoplantar keratoderma with deafness change single protein building blocks (amino acids) in connexin 26. The altered protein probably disrupts the function of normal connexin 26 in cells, and may interfere with the function of other connexin proteins. This disruption could affect skin growth and also impair hearing by disturbing the conversion of sound waves to nerve impulses.  Palmoplantar keratoderma with deafness can also be caused by a mutation in the MT-TS1 gene. This gene provides instructions for making a particular type of RNA, a molecule that is a chemical cousin of DNA. This type of RNA, called transfer RNA (tRNA), helps assemble amino acids into full-length, functioning proteins. The MT-TS1 gene provides instructions for a specific form of tRNA that is designated as tRNASer(UCN). This molecule attaches to a particular amino acid, serine (Ser), and inserts it into the appropriate locations in many different proteins.  The tRNASer(UCN) molecule is present only in cellular structures called mitochondria. These structures convert energy from food into a form that cells can use. Through a process called oxidative phosphorylation, mitochondria use oxygen, simple sugars, and fatty acids to create adenosine triphosphate (ATP), the cell's main energy source. The tRNASer(UCN) molecule is involved in the assembly of proteins that carry out oxidative phosphorylation.  The MT-TS1 gene mutation that causes palmoplantar keratoderma with deafness leads to reduced levels of tRNASer(UCN) to assemble proteins within mitochondria. Reduced production of proteins needed for oxidative phosphorylation may impair the ability of mitochondria to make ATP. Researchers have not determined why the effects of the mutation are limited to cells in the inner ear and the skin in this condition.