Problems in prenatal diagnosis of the ichthyosis congenita group.

The late onset of normal keratinization after week 24 menstrual age (MA) of fetal life is the cause of considerable problems with the prenatal diagnosis of congenital ichthyosis. This paper summarizes the experiences with prenatal diagnosis in nine pregnancies at risk of congenital ichthyosis and one at risk of chondrodysplasia punctata, rhizomelic type. An important prerequisite--and the main problem--is the manifestation of the mutant genes early enough in fetal life to allow a safe exclusion. Continuous precocious keratinization of the interfollicular epidermis, hyperkeratosis, and/or specific markers of congenital ichthyosis such as various types of lipid inclusions had been expected. With a normal ultrastructure and development of fetal epidermis no evidence of ichthyosis was present in eight cases; all eight children were born healthy. Regional variations of the onset of keratinization of the interfollicular epidermis, observed in one of these eight fetuses as well as in one fetus at risk (but normal for) recessive dystrophic epidermolysis bullosa, posed considerable problems and might lead to a false-positive diagnosis. Examination after birth allowed one to localize these regions to areas close to the mamillae. Regional variations in addition to the well-known cranio-caudal gradient thus are normal findings: both children have normal skin. One fetus at risk of non-bullous congenital ichthyosiform erythroderma (type II) was involved without prenatal manifestation of interfollicular keratinization, specific markers, or increased numbers of cornified cells in the pilosebaceous follicles at 20 weeks MA. A slightly more irregular pattern of the horn cell contents was not regarded as sufficient evidence alone to indicate congenital ichthyosis. A severely affected boy was born in week 34 MA. Similarly the fetus at risk of chondrodysplasia punctata showed no skin abnormalities, neither at fetoscopy (week 22 MA) nor after abortion (week 24 MA) although based on other clinical features it was clearly affected. Thus, this genodermatosis cannot be diagnosed prenatally by its keratinization disturbances. In future cases, precocious keratinization and hyperkeratosis cannot be expected to be expressed before week 24 MA, and minor signs, such as irregularities of horn cell contents, have to be taken as an indication of involvement. Multiple biopsies are required, and a safe exclusion may be impossible before week 22 MA.