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Autosomal recessive congenital ichthyosis (ARCI) represents a heterogeneous group of rare disorders of coz1r-nification with 3 major subtypes: harlequin ichthyosis (HI), lamellar ichthyosis (LI) and congenital ichthyosiform erythroderma (CIE). A 4th subtype has also been proposed: pleomorphic ichthyosis (PI), characterized by marked skin changes at birth and subsequently mild symptoms. In nationwide screenings of suspected cases of ARCI in Denmark and Sweden, we identified 132 patients (age range 0.1-86 years) classified as HI (n = 7), LI (n = 70), CIE (n = 17) and PI (n = 38). At birth, a collodion membrane or similar severe hyperkeratosis was reported in almost all patients with HI and LI, and in nearly half of patients with CIE and PI. Persistent ectropion was more common in HI (85%) and LI (57%), than in CIE (35%) and PI (5%). Anhidrosis was a frequent problem in all 4 groups (58-100%). A scoring (0-4) of ichthyosis/erythema past infancy showed widely different mean values in the subgroups: HI (3.2/3.1), LI (2.4/0.6), CIE (1.8/1.6), PI (1.1/0.3). Novel or recurrent mutations were found in 113 patients: TGM1 (n = 56), NIPAL4 (n = 15), ALOX12B (n = 15), ABCA12 (n = 8), ALOXE3 (n = 9), SLC27A4 (n = 5), CYP4F22 (n = 3), PNPLA1 (n = 1) and ABHD5 (n = 1). In conclusion, by performing a deep phenotyping and gene screening, ARCI can be definitely diagnosed in 85% of cases in Scandinavia, with a prevalence of 1: 100,000 and >8 different aetiologies.

Congenital ichthyosis is a collective name for a group of monogenetic disorders of cornification, sometimes associated with systemic symptoms. There may be an abnormal quality or quantity of scale produced, abnormal thickness of stratum corneum or abnormal keratinocyte kinetics, often associated with skin inflammation. Pruritus, skin fragility, ectropion and anhidrosis are sometimes associated with the rare types of ichthyosis. Three important mechanisms are involved in the action of topical agents used in the treatment of ichthyosis: hydration, lubrication and keratolysis. The latter effect can also be achieved with systemic retinoids. For ichthyosis with an increased tendency towards skin infections, antimicrobials are another group of widely used agents. Considering that patients with ichthyosis are potential mega-users of topical therapy, with an estimated lifetime consumption of approximately one tonne cream per capita, surprisingly few controlled trials of the various treatments have been performed. Moreover, nearly all therapeutic principles were established long before the recent increase in knowledge about the aetiology and pathophysiology of ichthyosis. This calls for new ideas and intensified efforts to develop future ichthyosis therapies.