Summation of ichthyosis, keratosis pilaris, palmar hyperlinearity and flexural eczema, to take into account all the skin features which may be associated with FLG null mutations, suggests a highly penetrant haploinsufficiency: 100% of individuals with two FLG null mutations and 87·8% of individuals with one FLG null mutation show one or more of these skin features, compared with 46·5% of wild-type individuals, a statistically significant difference (P< 0·0001, Fisher exact test). Here, FLG is linked to ichthyosis.