Ichthyosis vulgaris
This is the commonest form of inherited ichthyosis, affecting 1 in every 250 people. Ichthyosis vulgaris has been found to be due to a gene defect in filaggrin, which is a protein in the skin that impairs the skin barrier formation and the natural moisturising factors that are key to keeping the skin hydrated. It is usually quite mild and develops in early childhood with fine, light grey scales and roughness on the upper and lower limbs, but sparing the folds of the arms and legs. It may be more widespread and is more obvious in the winter time. It is sometimes associated with atopic or childhood allergic eczema and may cause an increased wrinkling of the palms and soles.
It can be treated with regular application of moisturisers. It improves in adult life and may be passed on to children whereby there is a 50:50 chance of each child having the disease (“autosomal dominant transmission”).
X-linked ichthyosis
This condition occurs in males only and develops in infancy with tan or grey scales on the limbs and across the trunk. It may affect the ears and face and the scales appear to be stuck on like stamps. It varies in its severity and improves in fine or sunny weather. It changes very little with age.
X-linked ichthyosis is due to lower levels of an enzyme known as steroid sulphatase. This condition is passed on by a mother, who is a carrier of the abnormal gene, to her son with a 50% risk for each son. A carrier mother shows no evidence of the condition. The gene that causes this condition has been identified and, very rarely, a similar fault can affect adjacent genes on the same chromosome, causing a variety of other problems for an affected male, for instance, bony defects or lack of the sense of smell.
A mother who is carrying an affected male baby may have a prolonged and consequently difficult labour. A small number of affected boys have poorly descended or undescended testicles; it is usual to check this aspect of development in affected families. The child’s growth should be monitored from time to time. It is quite common to have asymptomatic specks in the cornea that do not interfere with vision which are identified by an eye specialist.
Autosomal recessive congenital ichthyoses
There are three types of ichthyoses in this category: Congenital ichthyosiform erythroderma, Lamellar ichthyosis and Harlequin ichthyosis. These three conditions are passed on by parents with normal skin who both carry the abnormal gene (autosomal recessive) and the risk of a further child being affected is 1 in 4.
Congenital ichthyosiform erythroderma
This type of ichthyosis generally show signs at birth with the appearance of a collodion membrane on the newborn baby. This is a shiny yellow film stretched across the skin like a sausage skin. It dries out and gradually sheds within the first week of life. The “collodion baby” is nursed in a humidified incubator until the skin settles down. The majority of collodion babies will develop congenital ichthyosiform erythroderma. However, a small number of these babies will have normal skin once the membrane is shed and, therefore, it is not possible to accurately predict the outcome in the early stages.
Most collodion babies develop non-bullous ichthyosiform erythroderma, which literally means inflamed, scaly skin, without blisters. It affects 1 in every 300,000 births and so is very rare. Once the collodion membrane has shed, the skin remains red and has fine, white scales affecting the entire skin surface. In severely affected children the eyelids may be pulled outwards and there may be some mild scalp hair loss and tightness of the fingers. Because the skin is inflamed it will feel hot, even if the child is cold. Most children with this condition do not sweat normally and may overheat in hot weather, when exercising or with a fever. The palms and soles are sometimes thickened and scaly. Otherwise a child’s health is normal. They may suffer cosmetically and this is especially important when a child starts school, or in the teenage years.
Lamellar ichthyosis
Lamellar ichthyosis is a rare form occurring in 1 in 200,000 live births. Newborns usually present with a collodian membrane but the skin is different in that it is less red but the scaling is larger, perhaps darker and more adherent, or stuck down.
Harlequin ichthyosis
Harlequin ichthyosis is a very severe, but extremely rare type of inherited ichthyosis (approximately 5 per year in the UK). It is evident at birth due to the very thick scaling all over. Intensive care is required and detailed information on the condition will be needed for the parents and staff.
Bullous ichthyosis
Bullous ichthyosis also known as bullous ichthyosiform erythroderma, is another rare inherited ichthyosis. At birth the baby’s skin seems to be fragile and may show blisters, without much scaling. This causes severe problems for the young infant and intensive care is sometimes necessary in the first few weeks of life. A skin biopsy will be required early on to confirm the diagnosis. During the first year or two of life, the blistering tendency reduces but widespread redness, scaling and thickening of the skin becomes more obvious through childhood. This produces warty skin changes around the creases of the joints. Skin infections are quite common and can lead to a characteristic odour. There may be a reduction in sweating in childhood, which improves later in life. This is a troublesome and distressing condition for the child and the family.
It is transmitted as an autosomal dominant disorder, which means that one of the parents may be affected. However, in at least half of affected children, neither parent is affected; therefore the child has developed a new gene fault while growing in the womb. This means that there is no risk above the ordinary for further pregnancies in that family although the child may pass on the condition onto the next generation. Detailed genetic counselling is necessary.
Netherton’s syndrome
The incidence of this condition is not known but it is probably in the region of 1 in each 200,000 births in the UK. The newborn child is very red and has scaly or peeling skin. The infant is often underweight and slow to grow and this problem continues for the first year or two of life. The affected child may need prolonged hospital treatment until both the skin and the nutrition improve. A characteristic feature of Netherton’s syndrome is thin fragile scalp hair in the baby. Later it is spiky and this is an important clue to the diagnosis. In many affected children the skin improves in childhood, although it can flare up without warning.
Netherton’s syndrome is an autosomal recessive disorder where both parents are carriers and show no sign of the condition. There is however a risk to further babies of the order of 25%.
There are a number of other genetic or inherited forms of ichthyosis where there are other medical problems but these are so uncommon that they are not discussed here.
