White sponge nevus (WSN) is an

autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

dominant condition of the

oral mucosa The oral mucosa is the mucous membrane lining the inside of the mouth. It comprises stratified squamous epithelium, termed "oral epithelium", and an underlying connective tissue termed ''lamina propria''. The oral cavity has sometimes been descri ...

(the

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

lining of the mouth). It is caused by a mutations in certain genes coding for

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

, which causes a defect in the normal process of

keratinization Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

of the mucosa. This results in lesions which are thick, white and velvety on the inside of the cheeks within the mouth. Usually, these lesions are present from birth or develop during childhood. The condition is entirely harmless, and no treatment is required.

Signs and symptoms

It presents itself in the

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

, most frequently as a thick, bilateral, symmetrical white plaques with a spongy, corrugated or velvety texture. Most usually, the lesions are on the buccal mucosa, but sometimes on the labial mucosa,

alveolar ridge The alveolar process () or alveolar bone is the thickened ridge of bone that contains the tooth sockets on the jaw bones (in humans, the maxilla and the mandible). The structures are covered by gums as part of the oral cavity. The synonymous ter ...

, floor of the mouth, ventral surface of the tongue or soft palate. The

gingival margin The free gingival margin is the interface between the sulcular epithelium and the epithelium of the oral cavity. This interface exists at the most coronal point of the gingiva, otherwise known as the crest of the marginal gingiva. Because the sh ...

and dorsum of the tongue are almost never affected. Less commonly, sites outside the mouth are affected, including the nasal, esophageal, laryngeal, anal and genital mucosae. It usually is present from birth, or develops during childhood. Rarely, the lesions may develop during adolescence. Apart from the appearance of the affected areas, there are usually no other signs or symptoms.

Pathophysiology

WSN is caused by a mutation of the

keratin 4 Keratin, type I cytoskeletal 4 also known as cytokeratin-4 (CK-4) or keratin-4 (K4) is a protein that in humans is encoded by the ''KRT4'' gene. Keratin 4 is a type II cytokeratin. It is specifically found in differentiated layers of the mucosal a ...

keratin 13 Keratin 13 (or cytokeratin 13) is a protein that in humans is encoded by the ''KRT13'' gene. Keratin 13 is a type I cytokeratin, it is paired with keratin 4 and found in the suprabasal layers of non-cornified stratified epithelia. Mutations in ...

genes, located respectively at human

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

12q13 1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...

and 17q21-q22. The condition is inherited in an autosomal dominant manner. This indicates that the defective gene responsible for a disorder is located on an

autosome An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

(chromosomes 12 and 17 are autosomes), and only one copy of the defective gene is sufficient to cause the disorder, when inherited from a parent who has the disorder.

Diagnosis

Differential diagnosis

It is often mistaken for

leukoplakia Oral leukoplakia is a ''potentially malignant disorder'' affecting the oral mucosa. It is defined as "essentially an oral mucosal white lesion that cannot be considered as any other definable lesion." Oral leukoplakia is a white patch or plaque th ...

Classification

The

ICD-10 ICD-10 is the 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD), a medical classification list by the World Health Organization (WHO). It contains codes for diseases, signs and symptoms, ...

lists WSN under "other congenital malformations of mouth". It could be classified as a

skin condition A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this sy ...

, or more precisely as a

genodermatosis Genodermatosis is a hereditary skin disease with three inherited modes including single gene inheritance, multiple gene inheritance and chromosome inheritance. There are many different types of genodermatosis, the prevalence of genodermatosis rang ...

(a genetically determined skin disorder).

Treatment

There is no treatment, but because this is a benign condition with no serious clinical complications, prognosis is excellent.

References

External links

* {{Cytoskeletal defects Conditions of the mucous membranes Oral neoplasia Autosomal dominant disorders Rare diseases Cytoskeletal defects