The Lifelines cohort consists of many family relationships. During the inclusion into Lifelines, participants were asked if they had any family members who would be interested in joining the cohort. As a result Lifelines is one of the largest 3 generation cohorts available.

The basis of the family relations data within Lifelines consists of information from the municipal registries (Basisregistratie Personen (BRP)). Based on this information, researchers from the UGLI-consortium have optimized the family relations using recoded surname data (for privacy purposes) and data from questionnaires (Family composition). The process of this optimization has been documented and can be found here: Family relations reconstruction.

These optimized family relations were then verified by the UGLI-consortium using available genetic data. The most recent version of the family relations data (sec_family_relations_v3.1) has been verified by using genetic data from GWAS (CytoSNP), UGLI 1 (GSA), and UGLI 2 (Affymetrix). More detailed information on this process can be found in the quality control document of UGLI2-Affymetrix: QC_report_UGLI2_(release_1)-v1.pdf, page 6 - 9, section 6b and in the readme of the familyrelations.

In the latest version of the family relations data, couples who share a household, but don't have children, have also been included. This provides the opportunity to work on research involving environmental factors.

The data consists of 5 columns:

• Participant identifiers
• Family id
• Father identifier
• Mother identifier
• Gender
• Partner identifier

The identifiers can be used to pair the family data to other phenotypic and genotypic data. The same participant identifier can also be found in the column for father or mother and partner. This depends on the participant's family size and if they are, for example, both a child and a parent. Participants who have indicated to have family members who are not participating in Lifelines have also received a unique identifier, but this identifier can not be used to pair the data to other Lifelines data. An example of this is when two siblings have indicated to have the same parent. The identifiers of these family members, who are not participating in Lifelines, start with an 'S' (i.e. S1031206). The family id is used to identify participants that are part of the same family.

The latest version of family relations data has been verified using the collected genetic data from CytoSNP, UGLI-GSA, and UGLI2-Affymetrix. In the image below you can see a flow diagram of how this process has been performed: