Autosomal recessive congenital ichthyosis (ARCI) is a rare, heterogenous keratinization disorder of the skin, classically divided into two clinical subtypes, lamellar ichthyosis (LI) and nonbullous congenital ichthyosiformis erythroderma (CIE). Recently, strong evidence for the involvement of the transglutaminase 1 gene (TGM1) in LI has evolved. We have studied ARCI in the isolated Finnish population, in which recessive disorders are often caused by single mutations enriched by a founder effect. Surprisingly, five different mutations of TGM1 (Arg141His, Arg142Cys, Gly217Ser, Val378Leu, and Arg395Leu) were found in Finnish ARCI patients. In addition to affected LI patients, we also identified TGM1 mutations in CIE patients. Moreover, haplotype analysis of the chromosomes carrying the most common mutation, a C-->T transition changing Arg142 to Cys, revealed that the same mutation has been introduced twice in the Finnish population. In addition to this Arg142Cys mutation, three other mutations, in Arg141 and Arg142, have been described elsewhere, in other populations. These findings suggest that this region of TGM1 is more susceptible to mutation. The corresponding amino acid sequence is conserved in other transglutaminases, but, for example, coagulation factor XIII (FXIII) mutations do not cluster in this region. Protein modeling of the Arg142Cys mutation suggested disruption or destabilization of the protein. In transfection studies, the closely related transglutaminase FXIII protein with the corresponding mutation was shown to be susceptible to degradation in COS cells, further supporting evidence of the destabilizing effect of the Arg142Cys mutation in TGM1.

Autosomal recessive congenital ichthyosis (ARCI) is a group of inherited disorders of cornification in which progress has recently been made in the identification of pathogenic mechanisms causing the disease. Transglutaminase 1 (TGM 1) has been found as a defective gene in a large fraction of patients with lamellar ichthyosis (LI), a severe inherited scaling disorder of the skin. We have previously performed molecular genetic studies of 38 Finnish ARCI families and found six different mutations in 13 families of 38 (34%). In this study we compared the molecular genetic alterations with clinical and electron microscopic findings of these patients. Families were classified by electron microscopy in ichthyosis congenita (IC) types I, II, III, IV and a non-defined group. TGM 1 gene mutation was found in all of the IC type II and 1/3 of the IC type 1 families. Although electron microscopy is not always used to classify ARCI patients, it can distinguish groups which are parallel with molecular genetic findings. This finding might be useful in the classification of ARCI patients for further linkage studies. Clinically typical phenotype of the TGM1 mutation carrier includes large, thick, brownish scales, but ichthyosis of some of these patients tends to be milder.

Migrating keratinocytes actively involved in reepithelialization in dermal wounds acquire a collagenolytic phenotype upon contact with the dermal matrix. To determine whether this phenotype is associated with repair in other forms of wounds, we assessed collagenase expression in 50 specimens representing a variety of blistering skin diseases, including subtypes of epidermolysis bullosa, porphyria cutanea tarda, bullous pemphigoid, pemphigus, transient acantholytic dermatosis, and suction blisters. Distinct from that seen in chronic ulcers or in normal healing by second intention, reepithelialization in these blistering conditions was not necessarily associated with a complete loss of basement membrane, as determined by immunostaining for type IV collagen. Collagenase mRNA was detected in the basal keratinocytes of several specimens of epidermolysis bullosa simplex (six of 10) and of pemphigus (three of seven), as well as in one quarter of transient acantholytic dermatosis samples in the presence of an intact basement membrane. In contrast, three of nine porphyria cutanea tarda, one third of epidermolysis bullosa acquisita, and one of 10 bullous pemphigoid samples had collagenase-positive basal keratinocytes with the basement membrane disrupted. The collagenase-positive lesions generally represented older blisters with evidence of epithelial regeneration. Collagenase was also expressed in suction blisters at 2 and 5 d after induction of the blister, but was shut off when the epidermis had healed. Other metalloproteinases were expressed occasionally, if at all. Our results suggest that keratinocyte migration is associated with collagenase expression and that contact of keratinocytes with the dermal matrix is not necessarily needed for collagenase induction.

Background: Macular atrophy or anetoderma is a rare skin disease of unknown pathogenesis, characterised by wrinkled or flaccid skin. Objective: The finding of anetoderma in 5 patients followed up because of false-positive seroreactions of syphilis prompted us to study the occurrence of antiphospholipid (aPL) antibodies in anetoderma. Methods: 14 unselected patients with primary anetoderma (PA) were collected from hospital records and clinical, immunological and histological findings were compared in the two patient groups. Results: Of the 5 patients, 3 fulfilled the criteria for antiphospholipid syndrome. In two cases, it was secondary to systemic lupus erythematosus (SLE). Of the 14 PA patients 1 had aPL antibodies and 4 had borrelia antibodies. Two patients had thyroid antibodies; 1 of them developed SLE. In several biopsy specimens, microthromboses were seen in both patient groups. Conclusion: On the basis of this study and our previous findings, it seems that anetoderma is more often associated with aPL-positive SLE or lupus-like disease than with aPL-negative disease. Immunological mechanisms play an important role in both primary and secondary anetoderma. The meaning of false-positive serological tests for syphilis or borrelia and aPL antibodies is not clear, but they may be reacting to some still unidentified antigen. Probably, various systemic as well as local inflammatory and non-inflammatory processes, e.g. microthromboses, can trigger anetoderma via still unknown pathomechanisms.