The familial impact of sudden infant death syndrome: morbidity and mortality rates in siblings of children who died of sudden infant death syndrome

Background Sudden infant death syndrome (SIDS) remains a leading cause of death during the first year of life and is associated with multiple comorbidities, including inheritable cardiac diseases and psychiatric disorders. While the aetiology in most cases remains unknown, research indicates that genetic and environmental factors may have a role. Given that siblings share these risk factors, siblings of children who died of SIDS might not only have an increased risk for SIDS but may also be at higher risk for death later in life and other comorbidities. Purpose To determine whether siblings of children who died of SIDS have an increased risk of comorbidities and all-cause mortality compared to the general population. Methods This nationwide register-based cohort study used the Danish registers. We identified all infants who died of SIDS (through ICD-code, index case) in Denmark between January 1, 1977 and December 31, 2022 and their siblings (case) (Figure 1). All siblings were matched 1:5 by age and sex and followed from date of SIDS of the index case until diagnosis of comorbidities, death, emigration, or study end. Hazard ratios were calculated with Cox hazard regression models adjusted for sex, age, calendar year, and maternal education at index date. Results The study population consisted of 3,786 siblings from 1,480 SIDS index cases. The median age at baseline was 0.00 [IQR: 0.00-2.69] years, with a median follow-up time of 32 [IQR: 26-37] years and 51% of the siblings were male (Table 1). During the follow-up period, 249 (6.6%) siblings died of all-cause mortality (HR 2.2, 95% CI 1.70-2.92). We observed an increased risk of any psychiatric diagnosis (HR 1.5, 95% CI 1.34-1.57) and specifically for schizophrenia (HR 2.0, 95% 1.43-2.70) for siblings of children who died of SIDS. Conclusion In this nationwide study, having a sibling who died of SIDS was associated with a 2.2-fold increased risk of all-cause mortality at 32 years follow-up, a 1.5-fold increased risk of any psychiatric disease, and a 2.0-fold increased risk of schizophrenia compared to the general population. Shared genetic and/or environmental factors could explain this. Therefore, a family history of SIDS could be considered when assessing the risk of psychiatric disease.Fig 1.Flowchart selection cohort Tab 1.Baseline characteristics