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When skin structure or function fails

Epidermis

Disorders of keratinisation:

E.g. icthyoses
Caused by inherited genetic defects of protein synthesis
Produce scaly diseases

Blistering (bullous) diseases:

Characterised by the spontaneous or post-traumatic formation of blisters
Caused either by failure of the:

Desmosome – causing intra-epidermal blisters
Adhesion complex at the basement membrane zone – causing sub-epidermal blisters

May be inherited structural abnormalities (e.g. epidermolysis bullosa)
May be caused by the formation of antibodies against these proteins (e.g. pemphigus bullous pemphigoid)

Abnormalities of pigmentation:

Loss of melanocytes leads to depigmentation of the skin
E.g. vitiligo:

Common
Sometimes disfiguring
Can begin at any age

Abnormalities of DNA repair:

UV light causes damage to DNA after the first few months of life
Normally, DNA repair enzymes excise and repair the damaged strands
Xeroderma pigmentosa:

Is a rare inherited disorder which leads to a failure of this process
The result is accumulated damage to DNA and inevitable skin malignancies that are fatal before the age of 20 in 75% of patients

Loss of the whole epidermis:

This is seen in burns patients and after severe drug reactions (known as toxic epidermal necrolysis)
Leads to fluid and protein loss, failure of temperature regulation and susceptibility to infection

Adnexal structures (hair shafts, sweat glands, etc)

Absence of sweat glands:

Seen in a rare X-linked recessive condition called hypohidrotic ectodermal dysplasia
Characterised by:

Absent or reduced sweating
Hypotrichosis (absence of hair)
Partial anodontia (absence of teeth)

It causes heat intolerance and unexplained fevers in infancy or childhood

Abnormalities of hair:

Monilethrix – autosomal dominant and causes ‘beading’ of the hair
Alopecia areata – very common condition causing patchy hair loss. It is probably an autoimmune-mediated attack in which the hair follicle is surrounded by lymphocytes
Androgenetic alopecia – is age-related baldness which affects 54% of males and 24% of females over the age of 30. It is caused by a genetically-programmed alteration in metabolism of androgens by hair follicles

Dermis

Connective tissue disorders:

E.g. Ehlers-Danlos syndrome
Is caused by inherited abnormalities of collagen
Causes:

Fragility of the skin and blood vessels
Hyper-extensible skin
Joint hypermobilty

Patients develop:

‘Cigarette paper’ skin
Easy bruising
Recurrent joint dislocations
Spontaneous rupture of arteries
Spontaneous pneumothoracies


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	When skin structure or function fails Epidermis Disorders of keratinisation: E.g. icthyoses Caused by inherited genetic defects of protein synthesis Produce scaly diseases Blistering (bullous) diseases: Characterised by the spontaneous or post-traumatic formation of blisters Caused either by failure of the: Desmosome – causing intra-epidermal blisters Adhesion complex at the basement membrane zone – causing sub-epidermal blisters May be inherited structural abnormalities (e.g. epidermolysis bullosa) May be caused by the formation of antibodies against these proteins (e.g. pemphigus bullous pemphigoid) Abnormalities of pigmentation: Loss of melanocytes leads to depigmentation of the skin E.g. vitiligo: Common Sometimes disfiguring Can begin at any age Abnormalities of DNA repair: UV light causes damage to DNA after the first few months of life Normally, DNA repair enzymes excise and repair the damaged strands Xeroderma pigmentosa: Is a rare inherited disorder which leads to a failure of this process The result is accumulated damage to DNA and inevitable skin malignancies that are fatal before the age of 20 in 75% of patients Loss of the whole epidermis: This is seen in burns patients and after severe drug reactions (known as toxic epidermal necrolysis) Leads to fluid and protein loss, failure of temperature regulation and susceptibility to infection Adnexal structures (hair shafts, sweat glands, etc) Absence of sweat glands: Seen in a rare X-linked recessive condition called hypohidrotic ectodermal dysplasia Characterised by: Absent or reduced sweating Hypotrichosis (absence of hair) Partial anodontia (absence of teeth) It causes heat intolerance and unexplained fevers in infancy or childhood Abnormalities of hair: Monilethrix – autosomal dominant and causes ‘beading’ of the hair Alopecia areata – very common condition causing patchy hair loss. It is probably an autoimmune-mediated attack in which the hair follicle is surrounded by lymphocytes Androgenetic alopecia – is age-related baldness which affects 54% of males and 24% of females over the age of 30. It is caused by a genetically-programmed alteration in metabolism of androgens by hair follicles Dermis Connective tissue disorders: E.g. Ehlers-Danlos syndrome Is caused by inherited abnormalities of collagen Causes: Fragility of the skin and blood vessels Hyper-extensible skin Joint hypermobilty Patients develop: ‘Cigarette paper’ skin Easy bruising Recurrent joint dislocations Spontaneous rupture of arteries Spontaneous pneumothoracies
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