FGFR3 and acanthosis nigricans: SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) syndrome is caused by a lysine-to-methionine substitution at nucleotide 650 in the FGFR3 gene and is related to retarded development, the hyperpigmentation and hyperkeratosis of the skin (called acanthosis nigricans), anatomical abnormalities of the brain, epilepsy attacks and hearing loss [42].