Explain different types of keratin-related disorders

Keratins are a large family of structural proteins that form intermediate filaments in epithelial cells. They are mainly classified into Type I (acidic keratins) and Type II (basic keratins). These keratins work together to form stable filaments that give strength and resilience to epithelial tissues like skin, hair and nails. When mutations occur in keratin genes, the structure of intermediate filaments gets disrupted. This causes the cells to become fragile, leading to a group of genetic disorders known as keratinopathies or keratin-related disorders. Most keratin disorders are inherited in an autosomal dominant manner and each disorder shows specific symptoms depending on the tissue where the keratin is expressed.

There are many keratin-related disorders, but the most well-known include the following:

1. Epidermolysis Bullosa Simplex (EBS)

EBS is caused by mutations in the KRT5 or KRT14 gene. These keratins are present in the basal layer of the epidermis. Due to the mutation, the skin becomes very fragile and forms blisters easily after minor injuries, especially on the hands and feet. In severe forms, blistering can occur over large parts of the body. The disease mainly affects the stability of basal keratinocytes, which are responsible for maintaining the strength of the skin's lower layer.

2. Epidermolytic Hyperkeratosis (EHK)

EHK results from mutations in either the KRT1 or KRT10 gene. These keratins are expressed in the suprabasal layer of the epidermis. The main symptoms are thickened and scaly skin along with blistering, which is often present from birth or early infancy. The mutation affects the connection between skin cells, making the upper layers of the skin weak and prone to damage, leading to a loss of normal skin integrity.

3. Pachyonychia Congenita (PC)

This disorder is caused by mutations in one of the following genes: KRT6A, KRT6B, KRT16, or KRT17. It primarily affects the nails, palms, soles and oral mucosa. Individuals suffering from PC show nail dystrophy, painful thickened skin on palms and soles, white patches in the mouth and sometimes cysts under the skin. The disorder results from poor keratinocyte differentiation, leading to weak structural support in affected epithelial areas.

4. Monilethrix

Monilethrix is associated with mutations in KRT81, KRT83, or KRT86 genes which are mainly found in hair shaft keratin. The main symptom of this disorder is brittle, beaded hair that breaks easily, leading to sparse hair on the scalp. The mutation affects the strength and continuity of the hair shaft due to poor keratin fiber formation, making hair highly breakable and uneven.

5. Steatocystoma Multiplex

This condition occurs due to a mutation in the KRT17 gene and affects the sebaceous glands of the skin. Individuals with this disorder develop multiple sebaceous cysts, especially on the chest, arms and trunk. The mutation affects the proper development of the sebaceous duct lining cells, leading to cyst formation due to abnormal keratin accumulation.





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