Mutation in CUL4B observed in the present X-linked ID (XLID) case. (a) Partial sequence chromatograms of exon 22 of CUL4B in a patient and his mother. Red arrowheads denote the mutated base. The DNA and corresponding amino acid sequences of the wild-type and mutant CUL4B alleles are also shown. (b) A schematic representation of the CUL4B protein (top) and multiple alignment of the CUL4B amino acid sequences within the CULLIN-1 cullin family signature (bottom). Arrowheads denote the mutated amino acid. Amino acids that did not match those in Homo sapiens are shaded.