History
A 28-year-old man attends your clinic with his girlfriend. He has had dry skin since birth, although it has been worse since he became a teenager. His skin is generally itchy and requires regular application of emollients and vigorous twice-weekly exfoliation while washing. He is otherwise fit and healthy and a well-adjusted individual. He is planning to get married and would like information about the risk of his children being affected with the same skin condition. He knows other family members who are similarly affected. There is no history of consanguinity. He reports that all affected children were born by emergency caesarean section after very long labour (Fig. 95.1).
Examination
On examination he has normal teeth, hair and nails. He has generally dry skin with prominent adherent grey-brown scales over the extensor surfaces of his neck and limbs(Fig. 95.2). He has adherent bran-like scale throughout his scalp. There is no erythro-derma or blistering. His hands and feet are almost unaffected, with little scale and no hyperlinearity or keratoderma.
Questions
• What is the diagnosis and pattern of inheritance?
• How would you advise this couple about risk to a future generation?
Medicine
This case is a presentation of X-linked ichthysosis. In this condition dryness and scali-ness of the skin is often present from birth, and gradually becomes more prominent in late childhood. The build-up of adherent scale imparts a ‘dirty appearance’ to the skin.
Typically, the ichthyosis involves particularly the posterior neck, upper trunk, and exten-sor surfaces of the extremities, with sparing of the flexures as well as palms and soles (palmoplantar hyperlinearity is a feature of ichthyosis vulgaris). It is one of the most fre-quent enzyme disorders in humans with an incidence of approximately 1 in 6000 males.
It is due to a deficiency of steroid sulphatase (STS), which leads to epidermal barrier defect and corneocyte (or essentially scale) retention. Most affected individuals regard it as an annoyance, although it can be emotionally challenging in childhood and adolescence. Cryptorchidism can be associated in up to 20 per cent of cases. STS deficiency slows the delivery of an infant because of insuf-ficient cervical dilatation. A relative failure occurs in the response to intravenous oxy-tocin. Since both are indications for caesarean delivery or forceps delivery, an increased perinatal morbidity and mortality may occur.
Other differential diagnoses to consider include ichthyosis vulgaris (associated with pal-mar hyperlinearity, atopy and an autosomal dominant inheritance pattern) and lamellar ichthyosis (autosomal recessive inheritance). The diagnosis of X-linked ichthyosis can be confirmed by biochemical assay of STS and by genetic testing. You can reassure the patient that his sons will not be affected, however his daughters will be obligate carriers. His extended family would benefit from genetic counselling and advice. In particular his female relatives should inform obstetric teams about the possible complications related to prolonged labour or delayed delivery.
KEY POINTS
• X-linked ichthyosis is caused by steroid sulphatase deficiency.
• The condition is managed with emollients, keratolytics and mechanical exfoliation, with most patients considering it to be an annoyance without significant morbidity.
• It is associated with prolonged labour and, less commonly, cryptorchidism.
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