Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…(germline mutations) of many of the individual HDACs occurred to be lethal, either during embryonic or very early postnatal development with deleterious effects on distinct tissues or cellular processes recognized as the proximal cause of death (Lagger et al., 2002; Haberland et al., 2009a,b).
Category: