Immunoglobulin single variable domain binding to serum albumin having: (a) a CDR1 according to Abm that is chosen from the following sequences: GFTFSTGEMA (SEQ ID NO: 8) and GFTFDTSSML (SEQ ID NO:13) and that is preferably GFTFDTSSML (SEQ ID NO:13); and (b) a CDR2 according to Abm that is chosen from the following sequences: SISSSGATTY (SEQ ID NO:9) and VIHQSGTPTY (SEQ ID NO:14) and that is preferably VIHQSGTPTY (SEQ ID NO:14); and (c) a CDR3 according to Abm that is chosen from the following sequences: PRHPQGGVTFDY (SEQ ID NO:7), FPSTHGKFDY (SEQ ID NO: 12) and FPSSRMKFDY (SEQ ID NO: 15) and that is preferably FPSTHGKFDY (SEQ ID NO: 12) or FPSSRMKFDY (SEQ ID NO: 15) and that is most preferably FPSSRMKFDY (SEQ ID NO: 15); wherein said immunoglobulin single variable domain has no more than 7, such as no more than 5, preferably no more than 3, such as only 3, 2 or 1 amino acid differences in the frameworks compared to the amino acid sequence of SEQ ID NO: 1, not taking into account any mutations at position(s) 11, 89, 110 or 112 according to Kabat that may be present and not taking into account any C-terminal extension that may be present; in which: - the amino acid residue at position 11 is preferably chosen from L or V; and - the amino acid residue at position 89 is preferably suitably chosen from T, V or L; and - the amino acid residue at position 110 is preferably suitably chosen from T, K or Q; and - the amino acid residue at position 112 is preferably suitably chosen from S, K or Q; such that (i) position 89 is T; or (ii) position 89 is L and position 11 is V; or (iii) position 89 is L and position 110 is K or Q; or (iv) position 89 is L and position 112 is K or Q; or (v) position 89 is L and position 11 is V and position 110 is K or Q; or (vi) position 89 is L and position 11 is V and position 112 is K or Q; or (vii) position 11 is V and position 110 is K or Q; or (viii) position 11 is V and position 112 is K or Q; and wherein said immunoglobulin single variable domain has reduced binding by pre-existing antibodies present in serum from patients with SLE compared to SEQ ID NO: 1. (a) a CDR1 according to Abm that is chosen from the following sequences: GFTFSTGEMA (SEQ ID NO: 8) and GFTFDTSSML (SEQ ID NO:13) and that is preferably GFTFDTSSML (SEQ ID NO:13); and (b) a CDR2 according to Abm that is chosen from the following sequences: SISSSGATTY (SEQ ID NO:9) and VIHQSGTPTY (SEQ ID NO:14) and that is preferably VIHQSGTPTY (SEQ ID NO:14); and (c) a CDR3 according to Abm that is chosen from the following sequences: PRHPQGGVTFDY (SEQ ID NO:7), FPSTHGKFDY (SEQ ID NO: 12) and FPSSRMKFDY (SEQ ID NO: 15) and that is preferably FPSTHGKFDY (SEQ ID NO: 12) or FPSSRMKFDY (SEQ ID NO: 15) and that is most preferably FPSSRMKFDY (SEQ ID NO: 15); in which: - the amino acid residue at position 11 is preferably chosen from L or V; and - the amino acid residue at position 89 is preferably suitably chosen from T, V or L; and - the amino acid residue at position 110 is preferably suitably chosen from T, K or Q; and - the amino acid residue at position 112 is preferably suitably chosen from S, K or Q; - the amino acid residue at position 11 is preferably chosen from L or V; and - the amino acid residue at position 89 is preferably suitably chosen from T, V or L; and - the amino acid residue at position 110 is preferably suitably chosen from T, K or Q; and - the amino acid residue at position 112 is preferably suitably chosen from S, K or Q; such that (i) position 89 is T; or (ii) position 89 is L and position 11 is V; or (iii) position 89 is L and position 110 is K or Q; or (iv) position 89 is L and position 112 is K or Q; or (v) position 89 is L and position 11 is V and position 110 is K or Q; or (vi) position 89 is L and position 11 is V and position 112 is K or Q; or (vii) position 11 is V and position 110 is K or Q; or (viii) position 11 is V and position 112 is K or Q; and wherein said immunoglobulin single variable domain has reduced binding by pre-existing antibodies present in serum from patients with SLE compared to SEQ ID NO: 1. (i) position 89 is T; or (ii) position 89 is L and position 11 is V; or (iii) position 89 is L and position 110 is K or Q; or (iv) position 89 is L and position 112 is K or Q; or (v) position 89 is L and position 11 is V and position 110 is K or Q; or (vi) position 89 is L and position 11 is V and position 112 is K or Q; or (vii) position 11 is V and position 110 is K or Q; or (viii) position 11 is V and position 112 is K or Q; and