IVS 1-5 (G-C) mutation in beta globin gene causing b-thal is phenotypically beta 'plus'.

Reference: Barbara J. Bain. Hemoglobinopahty Diagnosis. Blackwell Publication. 2nd Ed. p89.

Regarding the 2nd part of the question you have to search papers around for such reports.

IVS 1-5 (G-C) is a severe beta+ mutation

HbVar is an exhaustive data bank of all the documented mutations in the globin genes either for Hb variants or Thal mutations.

You may find it useful to consult: any time you find a new mutation

http://globin.bx.psu.edu/hbvar/

Specifically, description of IVS 1-5 (G-C) is to be found at:

http://globin.bx.psu.edu/cgi-bin/hbvar/query_vars3?mode=output&display_format=page&i=824

Thank you

IVS 1-5 (G-C) mutation causes a beta plus phenotype. Homozygotes for this mutation are affected by intermedia thalassemia while double heterozygotes for HbS / IVS-1-5 (G-C) are affected by thalassodrepanocitosis with a genotype betaS/beta +