GSTM1 and autosomal dominant cerebellar ataxia: This study reveals that most cases of SCA in Jazan have [−/−] Xmn1 having higher levels of Hb F and positive Xmn1 ′5 to Gγ, which is normally associated with a significantly low level of Hb F compared with negative Xmn1 ′5 to Gγ.