SGCB and limb-girdle muscular dystrophy: Bi-allelic mutations in the genes of each sarcoglycan cause specific subtypes of recessive LGMD: mutations on the a-SG gene (SGCA) lead to LGMDR3, on the b-SG gene (SGCB) to LGMDR4, and on the c-SG gene (SGCC) to LGMDR5 (3), while mutations on the d-SG gene have been discovered to cause the extremely rare LGMDR6 (4).