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Lamellar ichthyosis (LI) is a keratinization disorder characterized by the presence of large scales all over the body without significant erythroderma.
It is the most common variant of autosomal recessive congenital ichthyosis (ARCI; see this term). Prevalence is estimated approximately at 1/100,000-1/1,000,000 individuals.
Newborns are often encased in a collodion membrane (taut, shiny, translucent membrane appearing as an extra skin layer) with ectropion and eclabium. Once the membrane has been shed (after one-two weeks), scales covering the whole body become apparent. In classic LI, scales are large, dark and plate-like. Milder forms with lighter and thinner scales are possible. Contrarily to congenital ichthyosiform erythroderma (CIE), there is no significant erythroderma. Nevertheless, LI and CIE are the two extremities of a same spectrum with many patients exhibiting intermediate phenotypes. Furthermore, patient's phenotypes may change over time or under treatment. Skin is usually itchy or painful (cracks), mobility can be reduced due to skin stiffness and the sensitivity may be reduced by skin thickness. Other associated features include: persistent ectropion and associated eye complications (keratitis, corneal scarring), nail dystrophy, scarring alopecia, palmo-plantar keratoderma, failure to thrive, short stature, hypohidrosis with heat intolerance, and hearing defects (due to the accumulation of scales in the external ear).
LI is a genetically heterogeneous disease. It is due to mutations in genes TGM1, ABCA12, ALOX12B, and NIPAL4. Most mutations are found in the TGM1 gene encoding transglutaminase 1, involved in the formation of the epidermal cornified cell envelope. ABCA12 encodes an ATP-binding cassette (ABC) transporter, involved in lipid transport, ALOX12B codes for arachidonate 12(R)-lipoxygenase involved in lipid metabolism, and NIPAL4 likely encodes a membrane receptor. There is no clear genotype-phenotype correlation.
The diagnosis is based on the clinical appearance of the skin. Histological aspect of the skin is not specific. Molecular testing is possible but is not available in general practice. Immunohistochemistry using antibodies directed against TGase 1 or TGase 1 enzyme activity measurement is available in some centers.
Differential diagnoses include syndromic forms of ichthyosis, recessive X-linked ichthyosis and autosomal dominant ichthyosis vulgaris in mild forms, and CIE in case of erythroderma (see these terms). The disease is transmitted as an autosomal recessive trait.
Prenatal diagnosis is based on DNA analysis of amniocentesis and chorion villus sampling materials. Ultrasonography can detect the collodion membrane.
Genetic counseling should be offered to the affected families informing them of the 25% risk of recurrence.
Management and treatment
Management is based on daily applications of emollients or keratolytics. Oral retinoids are useful in severe forms (usually more than 35 mg/d in adults, 0.7 mg/kg/d in children).
Prognosis is variable. During the neonatal period, there is a risk of sepsis and hydro-electrolytic troubles. The disease often remains stable over the life, with periods of exacerbation. The life expectancy is normal. The disease has a strong impact on the quality of life due to the altered physical appearance, the troublesome symptoms, and the constraints due to disease and the treatment.