There are a vast number of hereditary skin diseases. Examples of hereditary skin diseases and the clinical approach are summarised in Tables 46.1 and 46.2.

Ichthyoses

These are a group of inherited disorders resulting in abnormal keratinisation, differentiation and desquamation of the epidermis (Table 46.3). They are characterised by generalised scaling of the skin to varying degrees from mild (ichthyosis vulgaris) to severe life-threatening (harlequin ichthyosis). Ichthyoses usually present at birth, in the neonatal period or early infancy. Presence or absence of erythroderma or blistering, distribution and features of the scale help to differentiate between the ichthyoses.

Diagnosis can often be made clinically and confirmed by the characteristic histological features on skin biopsy ± DNA analysis to identify disease causing mutation(s) ± biochemical analysis for defect in disease-causing molecules.

Treatment is symptomatic, aimed at decreasing the hyperkeratosis: topical emollients, keratolytics (10% urea or 5% salicylic acid), retinoids. Oral retinoids (acitretin) may dramatically improve some forms of ichthyosis. However, the benefits of life-long use need to be weighed against its potential side effects and use in women of child-bearing age (teratogenic).

Epidermolysis Bullosa

A group of inherited disorders where different disease-causing mutations result in defects in the structural proteins of the basement membrane (see Chapter 17, Figure 17.1). Characterised by skin fragility and blistering following minor trauma, ulceration and infection of wounds followed by scarring.

Mucosal surfaces may be affected: eyes, gastrointestinal tract (e.g. dysphagia due to oesophageal strictures may lead to nutritional deficiencies and complications such as iron-deficiency anaemia).

There are three main types, with many subtypes of varying severity according to the level of blister formation in the skin (Table 46.4).

Diagnosis is made clinically and confirmed by the characteristic electron microscopic features on skin biopsy and DNA analysis.

Treatment is supportive and aimed at:

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