The present invention relates to naturally-occurring growth hormone mutations; to a method for detecting them and their use in screening patients for growth hormone irregularities or for producing variant proteins suitable for treating such irregularities. In one aspect there is disclosed variants of GH1, selected from the group consisting of: (a) (i) +480 C→T; (ii) +446 C→T; (iii) +1491 C→G; (iv) −60 G→A; (v) −40 to −39 GG→CT; (vi) −360 A→G; and (vii) +748 A→G (where figures relate to GH1 nucleotide position number, counting from TSS); (b) a sequence substantially homologous to or that hybridises to sequence (a) under stringent conditions; (c) a sequence substantially homologous to or that hybridises to the sequences (a) or (b) but for degeneracy of the genetic code; and (d) an oligonucleotide specific for any of the sequences (a), (b) or (c) above.