The first mechanism has been ascertained only in eight cases of male with Klineferter syndrome with XXY chromosomes and IP phenotype [16,17,18,19,20,21,22,23]; the second mechanism, a somatic mosaicism for the NEMO LoF mutation, has been proposed for the majority of IP males as the only possible cause of the disease [24,25]. This evidence concerns the gene IKBKG and incontinentia pigmenti.