Participants and sample collection and DNA extraction

The study was approved by the Human Research Ethics Committee (HREC; Medical) of the University of the Witwatersrand, Johannesburg (Protocol number: M120223). Three groups of participants were enrolled and venous blood was collected into tubes containing EDTA anticoagulant. Inclusion criteria were as follows: male, over the age of 18 years, four grandparents who speak the same language as the participant (in the Bantu-speakers in order to avoid recently admixed individuals), not known to be related to the other participants in the study, and willing to provide broad informed consent (including consent to share data and DNA for future studies approved by the HREC (Medical)). Where feasible, community engagement preceded enrollment. Three main ethnolinguistic groups were included in this SAHGP pilot study. Individuals self-identified in terms of the ethnolinguistic group as part of the recruitment process. Group 1: individuals of mixed ancestry (referred to as COL in the South African context) were recruited through the Western Province Blood Transfusion Service by Sister Debbie Joubert under the guidance of Professor Soraya Bardien. Group 2: Sotho (Sotho-Tswana-speakers): seven individuals in this group were recruited from in and around the town of Ventersburg in the Free State Province, following community engagement done by Professor Michèle Ramsay and recruitment by Mr. and Mrs. Botha and Mrs. van den Berg. Group 3: Xhosa-speakers (Nguni language): eight individuals were recruited by Dr Nomlindo Makubalo from her medical clinic in the Eastern Cape Province. One individual was a Zulu-speaker (Nguni language) from Johannesburg. All DNA samples were extracted in the same laboratory using a modification of the salting out procedure⁷¹. The DNA was normalized and sent to the service provider (Illumina Fast Track) as a single batch at the same time, and all the data were returned in one batch.