The proportion of family relatives fulfilling informal caregiving roles varies across cultures and countries, and may be changing in most societies. Nonetheless, at least in Southern Europe, secondary caregivers of patients with dementia or severe mental illness are often relatives. As compared to primary caregivers (often key-relatives of the patient), these other informal caregivers have been under-studied and are less likely to be engaged in family interventions.

A few studies in dementia suggested that primary caregivers were overburdened as compared to other caregivers. One study in schizophrenia did not find such differences. Recent Portuguese data concern the FAMIDEM study (n=180), where a comparison of a number of dyads of keyrelatives and other relatives of the same patients with dementia was conducted. Comprehensive assessments included objective and subjective burden, psychological distress and positive aspects of caregiving. Important issues were raised, namely a word of caution on underestimating the risks of ‘second-line’ caregiving.

In practice, most evidence-based family interventions, either psychoeducational or not, rely on the active engagement of several family members, and not only of primary caregivers. Notorious examples in the field of severe mental illness include the behavioural family approach according to the Falloon's model, multiple family groups as proposed by McFarlane, and Kuipers, Leff & Lam's expressed emotion-focused family work. The same obviously applies to family systems approaches, in schizophrenia, bipolar disorder or in dementia.

Despite contradictory evidence, the experience of secondary informal caregivers and non-key relatives should be taken into account while planning family work.