Acknowledgements
We are highly grateful to the members of family NMD02 and ID01 for their participation and co-operation in the study. We thank Dr. JG Leroy for helpful comments. One author (NA) was a recipient of an indigenous and an IRSIP scholarship from Higher Education Commission, Pakistan. This study was supported by personal funds (NM), NIMAD research grant (940714) awarded to MAF, Swedish Research Council (OM), Academy of Finland (OM), Sigrid Jusélius Foundation (OM) and a grant from Koshish Foundation, USA (SN).