Brief definitions for words that relate to Pachyonychia Congenita and its symptoms.

ANGULAR CHEILITIS: sores at the corner of the mouth.

CELL: The basic building block of all living things. The nucleus of a cell contains DNA.

CHROMOSOMES: Genes are packaged in bundles called chromosomes. Humans have 23 pairs of chromosomes (for a total of 46). Of those, 1 pair is the sex chromosomes (determines whether you are male or female, plus some other body characteristics), and the other 22 pairs are autosomal chromosomes (determine the rest of the body’s makeup). (Source – Mary Kugler, R.N.)

CLINICAL DIAGNOSIS: a diagnosis based on the examination of the physical condition and clinical features of the patient.

CYST: a closed pocket or pouch of tissue. It can be filled with air, fluid, pus, or other material. Types of cysts associated with PC include:

  • STEATOCYSTOMA: cysts that are usually pea-sized or smaller, and flesh- or yellow-colored. They are usually on the chest, neck, or face and may drain a clear, yellow, oily fluid. They are not usually painful.
  • PILOSEBACEOUS: cysts on the scalp, armpits, groin or back. They may often drain a cheesy, sometimes foul smelling or pussy-looking material. These often become painful and inflamed.
  • FOLLICULAR HYPERKERATOSIS: groups of bumps that form around hair follicles, usually on the outer arms, thighs, waist or buttocks.

DNA (deoxyribonucleic acid): substance within a cell that carries a person’s genetic information. DNA is made up of four similar chemicals (called bases) that are repeated over and over in pairs.

DOMINANT: one copy of a gene causes the condition.

ENZYMES: proteins that are produced by the body’s cells and cause biochemical reactions to occur.

EPIDERMIS: the tough, protective outer layer of skin which is most affected in PC.

GENES: a part of the DNA that contains “instructions” telling the body how to produce specific proteins. Human beings have about 25,000 genes.

GENETIC DIAGNOSIS: a diagnosis based on determination of the specific mutation in the genes KRT6A, KRT6B, KRT6C, KRT16 or KRT17. A genetic diagnosis can only be made through genetic testing.

GENOTYPE: the genetic information from your DNA.

HUMAN GENOME: The human genome is a complete copy of the entire set of human gene instructions. The Human Genome Project, completed in 2003, identified all the human genes in DNA and stored the information in databases so all researchers everywhere could use it.

HEREDITARY MUTATION: genetic mutation occurring when one or both parents has PC; also referred to as inherited or familiar mutation.

HYPERKERATOSIS: a thickening of the outer layer of the skin resulting from the body producing an excess of proteins called keratins.

HYPERTROPHIC: abnormal increase in size of a body part (in PC, this usually refers to fingernails or toenails).

KERATODERMA: thickening of skin (palmoplantar = on palms & soles).

KERATIN: tough, fibrous proteins that form the main structure of hair and nails.

LARYNX: commonly called the voice box. Laryngeal means related to the larynx.

LEUKOKERATOSIS: white film caused by excess keratin on the tongue and inside cheeks.

MUTATION: a permanent change in the DNA sequence (code) of a gene. A mutation may be disease-causing or harmless.

NAIL DYSTROPHY: fingernails and/or toenails that do not form correctly.

ONYCHOSIS: any disease or disorder of the nails.

ORAL MUCOSA: inside the mouth.

PALMAR: having to do with the palms on the hands.

PHENOTYPE: the physical appearance of a particular genetic trait, or how symptoms look and feel.

PROTEINS: chains of chemical building blocks called amino acids. Proteins form the basis for most of what the body does, such as digestion, making energy and growing. (Source – Mary Kugler, R.N.)

PLANTAR: having to do with the soles of the feet.

POLYMORPHISM: a harmless, permanent change in the DNA sequence (code) of a gene.

RNA: messenger carrying instructions from DNA for controlling proteins.

RECESSIVE: a person must have two copies of a gene with a mutation to have a condition.

SPONTANEOUS MUTATION: mutation occurring when no parent or other family member has PC.


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What are Genes, DNA and Chromosomes?” — A great resource for understanding more about the basics of genetic diseases.


Pronounced   "Pack-e-o- neek-e- uh"   "kuhn-jen-i-ta"

PC is an ultra-rare (orphan) genetic skin disorder caused by a single mutation in any one of five keratin genes KRT6A, KRTK6B, KRT6C, KRT16, or KRT17.

pachy means thick
onychia refers to nails
congenita means something present at birth