Congenital ichthyosiform erythroderma mimicking ichthyosis bullosa of Siemens

Bullous congenital ichthyosiform erythroderma (BCIE) is a severe autosomal dominant inherited skin disorder caused by keratin 1 (K1) gene (KRT1) or keratin 10 (K10) gene (KRT10) mutations. Patients with BCIE show generalized erythema and bullae from birth. Histopathologically, granular degeneration is seen in the middle to upper epidermis. Keratin clumps predominantly comprising K1 and K10 are observed in the spinous and granular layers.Ichthyosis bullosa of Siemens (IBS) is a relatively mild ichthyosis with superficial blister formation caused by keratin 2e (K2e) gene (KRT2E) mutations and in which granular degeneration is restricted to the uppermost spinous and granular layers. Patients with IBS who had severe skin phenotypes and who had previously been misdiagnosed with BCIE from their clinicopathological findings were correctly diagnosed by molecular genetic testing methods. Conversely, here we report a family with mild BCIE showing clinical and histological features similar to IBS. A heterozygous missense mutation p.Glu478Asp in KRT1 was detected in this family.We previously reported that the differential diagnosis of IBS and BCIE is difficult in some instances and molecular genetic testing is useful to differentiate IBS from BCIE. In the present report, we show that p.Glu478Asp in K1 leads to clinicopathological features mimicking IBS, i.e. superficial blisters and granular degeneration restricted to the uppermost spinous and granular layers of the epidermis. These results further confirm that there are many cases of BCIE and IBS in which the correct differential diagnosis is problematic unless mutational analysis is performed.© 2007 British Association of Dermatologists