He had no hyperlaxity or arachnodactyly, and established causes of tall stature (Klinefelter syndrome, pituitary gigantism, hyperthyroidism, and genetic aberrations of the CNP-NPR2 axis) were excluded by karyotype, serum (normal IGF-I, IGFBP-3, FSH, LH, testosterone, FT4 and TSH) and candidate gene analysis (NPPB, NPPC, NPR2 and NPR3). The gene discussed is CNP; the disease is Klinefelter syndrome.