Genodermatoses mean skin diseases related to genetics.
Ichthyosis: means dry and scaly skin. This term is derived from Greek word ichthys, meaning (fish).
Types of ichhthyosis:
Ichthyosis vulgaris. 1.
2.X-linked ichthyosis.
3.Epidermolytic hyperkeratosis (Bullous congenital ichthyosiform erythroderma), Autosomal dominant .
4. Autosomal recessive ichthyosis: non- bullous congenital ichthyosiform erythroderma& lamellar ichthyosis.
5. Harlequin ichthyosis, Autosomal recessive.
6.Erythrokeratodermia variabilis , Autosomal dominant .
7. Ichthyosis Linearis circumflexa, Autosomal recessive.
Ichthyosis vulgaris:
Inheritance: Autosomal dominant .
Incidence:1:250.
Onset: Early childhood ,usually between 3-12 months of age .
Scales: fine ,brany scales, pasted –on over the entire body.
The scales are coarser on the lower extremities than they are on the trunk .
Varying degrees of dryness of the skin may be evident .
Distribution: the extensor surfaces of the extremities are most prominently involved .The flexures (axillary,gluteal folds,antecubital and popliteal fossae) are usually spared.
Accentuated skin markings and hyperkeratosis of the palms are common features.
Associated features: Atopy and keratosis pilaris.
Histopathology: hyperkeratosis and absence of granular layers.
Natural course: The patient improves in summer and gets worse in winter .
There is some improvement with age, so appears in infancy and improves in adulthood.
X-linked ichthyosis.
Inheritance: X-linked recessive, usually affect males .If a carrier female XX married affected male XY, so the female could have the disease .However ,carrier female may show milder degree of the disease .
Incidence:1:2000-6000.
Onset: since birth.
Scales: are larger and darker than I. vulgaris scales
Distribution: Generalized ,the extensors and the flexures are involved ,while in I. vulgaris involves extensors only.
The side of the neck are invariably involved .The palms and soles are nearly always spared .
Associated features:
1.Corneal opacities in 50% of patients.
2.There is an enzyme deficiency in fibroblasts and keratinocytes :steroid sulfatase. The action of this enzyme is to hydrolyse cholesterol sulfate in the stratum corneum ,so if cholesterol sulfate remains, it increases cohesion of corneocytes and decreases shedding so leads for thickening and roughness of the skin.
Diagnosis is by lipoprotein electrophoresis: LDL is high .
3.Because patients with XLI are deficient in steroid sulfatase ,delayed labour may occur ,because this enzyme enhances labour .The baby is delivered covered by collodian membrane .
Histopathology: Hyprkeratosis and hyper granulosis.
Natural course: There is no seasonal variation and not improved with age.