Ichthyosis Vulgaris : This is the most common of these disorders. It is inheritedas an autosomal dominant character and is characterized by an inability to shed stratum corneum. The lesions firstappear after the first year of life and consist of largebrownish angulated scales present all over the body,sparing the face and the flexural folds such as the cubitaland the popliteal fossae, axillae and groins. The scales aremore prominent on the extensor surfaces. Some patientsmay also have small hyperkeratotic follicular papules(keratosis pilaris) especially over the shoulders and thebuttocks, and the palms and soles may also show increasedlinearity or even diffuse hyperkeratosis. The lesions areasymptomatic, improve during summer but worsen duringthe winter. There is some improvement at puberty thoughthe disease persists throughout life.
X-linked Ichthyosis : This is caused by a recessive gene located on the distalshort arm of the X-chromosome. It is transmitted by thefemales but manifested in the males, and thus it is commonto find the maternal uncle having the same disease.Clinically, it resembles ichthyosis vulgaris except that thescales have a characteristic stuck-on appearance, thescaling encroaches upto the folds of the cubital and thepopliteal fossae and also involves the sides of the face,keratosis pilaris is never found, the palms and soles arenormal and it does not improve at puberty. Comma shapedcorneal opacities developing between the age of 20-30years are common and undescended testes, under-developed genitalia or mental retardation may be associated.
Lamellar lchthyosis : It was previously known as non-bullous form of ichthyosiformerythroderma. It is inherited as an autosomalrecessive gene and therefore the disease is more commonif the parents belong to the same family (consanguinemarriage). The manifestations are present at birth and mayvary from a mild redness and scaling to a severe sheet-likeencasing over the entire body. The skin is smooth andshiny, the flexure surfaces of the joints are involved moreseverely and display characteristic transverse ridges, whilethe palms and soles show diffuse hyperkeratosis which mayextend onto the dorsal surfaces. Some patients haveectropion, eclabion or elongated narrow hands. There areno seasonal variations but the disease tends to becomemilder as the age advances. Erythema and scaling usuallyextend to involve the face and the scalp, and abnormalitiesof some other systems may also be associated. Theintensity of erythema and scaling vary from patient topatient.
Epidermolytic Hyperkeratosis :It is the rarest of these dermatoses. It was previously knownas the bullous variety of ichthyosiformerythroderma.Transmitted by an autosomal dominant gene, it manifestswith recurrent crops of bullous lesions on the body whichstart within the first few months after birth and progressively change into thick hyperkeratotic lesions especiallyon the flexure surfaces of the joints. Secondary infectionis common. Palms and soles may show diffuse keratoderma. Bullous lesions tend to stop recurring as the ageadvances but keratotic lesions continue throughout life.
Aetiopathogenesis : Ichthyosis vulgaris and X-linkedichthyosis are caused by an inability to shed stratumcorneum from the surface while the rate of epidermal cellproliferation is normal. Deficiency of the enzyme steroidsulphatase has been demonstrated in X-linked ichthyosisLamellarichthyosis and epidermolytic hyperkeratosis showan increased rate of epidermal cell proliferation which isresponsible for the formation of scales. Bullae in epidermolytic hyperkeratosis are spongiform.
Palmo-Plantar Keratoderma : Hyperkeratosis of the palms and soles may be the onlymanifestation in some cases or it may occur as a part andparcel of a skin disease such as ichthyosiformdermatoses,pityriasisrubrapilaris etc. Diffuse palmo-plantar keratoderma involves the entire surface of both the palms andsoles. The mode of inheritance is autosomal dominant insome cases, and autosomal recessive in others. In somecases, the keratoderma is limited to a localized area andmanifests as deep painful fissures which may be associatedwith bleeding and secondary infection.
In some other patients, the hyperkeratosis is limited tosmall punctate areas.
Several cases of hyperkeratosis of the palms and solesare not based on genetic mechanisms, these are caused bya variety of other agents/diseases.
EpidermolysisBullosa : This is actually a group of disorders characterised by atendency to develop blisters in response to routine minortrauma. The blisters and ulcers are therefore located on theareas subject to routine trauma especially the hands, feet,elbows and knees, and even in the mucous membranesThese disorders can be grouped into three major categories: (1) Epidermolytic types are inherited as autosomal dominanttrait and are generally the mildest. The blisters are formedin between the epidermal layers by degeneration of theprickle or basal cells, and healing occurs without scarring.The mucous membranes and nails are not involved; (2)Junctional forms are inherited as autosomal recessive traitand are characterised by the location of the split in thebasement membrane at the level of the lamina lucida. Thesetypes are usually more severe and have extensiveinvolvement of the skin, and the mucous membranes. Lossof the nails and teeth is also common. Some types are highlyfatal. The lesions however heal without scarring or miliaformation; (3) Dermolytic types include some forms whichare inherited as a dominant character while others arerecessive. The blisters form below the basement membraneand therefore scarring, milia formation, syndactyly, loss ofnails and teeth are common.
Freckles : This disease is transmitted by an autosomal dominant geneand manifests as 2-3 mm asymptomatic irregular brownishmacules which appear early in age and progressivelyincrease in number and size, but remain limited to the lightexposed parts of the body. Face and dorsal aspects of thehands and forearms are therefore commonly involved. Thelesions are caused by an abnormality of the melanocyteswhich produce large melanosomes.
LentiginesThese lesions clinically resemble freckles but are usually much darker and larger in size. These are also most profuseon the face but do not show darkening on exposure tosunlight.
XerodermaPigmentosum : This is an autosomal recessive disorder in which the abilityto repair the DNA damaged by ultraviolet light is impaired.The earliest manifestations occur during infancy and mayconsist of photophobia or erythema on the face. Later on,the patient develops dryness and freckle-like lesions on theface and other light-exposed areas. Subsequently, the lesionsspread to the unexposed areas as well though these arealways more numerous on the exposed parts. With progressive damage the patient also develops whitish atrophic spotsand telangiectasia. In addition, there is an increasedtendency to develop multiple and recurrent tumoursinclude basal and squamous cell epitheliomas, malignantmelanoma and even sarcomas. Majority of the casesterminate fatally even before puberty, though some cases(Xerodernoid) may live a normal span of life. Ocularmanifestations such as conjunctivitis, ectropion, symblepheron, pigmented macules on the conjunctiva, vascularpterygium, corneal opacities and ocular neoplasms, andmental retardation and microcephaly may also be associated.
Albinism : This is a group of disorders manifesting as completeabsence of melanin pigmentation in the.skin, hair and/orthe eyes which is present at birth and remains unchangedthroughout the life. The mode of inheritance in most ofthe patients is autosomal recessive. Absence of pigmentation in the skin leads to increased hypersensitivity to lightand tendency to develop malignancies, while absence ofpigment in the eyes produces photophobia and nystagmus