Other prominent TTD features in the epidermis, including acanthosis (thickening of the layer of the nucleated cells), hyperkeratosis (prominent thickening of the cornified layer), and pronounced granular layer and sebacious gland hyperplasia (causing greasy appearance of the hair), were absent in the skin of XpdTTD/†XPCS mice, as established by blind microscopic examination of skin sections (Figure 2B). Furthermore, anaemia and developmental delay present in patients with TTD [24] and in XpdTTD/TTD mice [15] were both partially rescued in compound heterozygous XpdTTD/†XPCS mice (Figure 2D and 2E).