Desmosomes and corneodesmosomes and their relevance to genetic skin diseases.

Desmosomes are critical intercellular junctions between keratinocytes in the living cell layers of the epidermis. When the cells are differentiated and become cornified cells, desmosomes are transformed into corneodesmosomes. Distribution patterns of corneodesmosomes change with cell development. Namely, in the lower stratum corneum, corneodesmosomes are seen all around the cell membrane, but in the upper layers, they are only found at the edges of the flattened cells. Recently, it has been proposed that tight junction-derived structures are involved in this unique distribution of corneodesmosomes by protecting corneodesmosome degradation from proteases. Various types of skin diseases can be caused by abnormalities in the genes encoding components of desmosomes and corneodesmosomes or regulators of the proteolytic processing of these structures. Their clinical symptoms vary greatly: palmoplantar keratoderma on the pressure points, syndromic ichthyosis associated with atopic manifestations, diffuse keratoderma with cardiomyopathy, lethal epidermolysis bullosa, hair abnormalities, or a combination of these symptoms. Polymorphisms in some of the genes are risk factors for atopic dermatitis. Genetic diseases of desmosomes and corneodesmosomes are rare, but by studying them we will be enlightened about pathological mechanisms of more common multifactorial skin diseases such as atopic dermatitis.