Clinical Context

Sudden infant death syndrome (SIDS) and sudden unexplained death in children (SUDC) are both defined by sudden unexpected, unexplained death however, SIDS refers to children younger than one year and SUDC refers to a children greater than one year old. Although the rate of SIDS in the US has declined in the past several decades, the prevalence of SIDS remains approximately twice as high among Black and American Indian/Alaska Native populations. In a previous review article by Adams and colleagues published in the June 1, 2015, issue of the American Family Physician, risk factors for SIDS were outlined.^[1] They found that the most important risk factors for SIDS involve the sleep environment; sleeping position, bed sharing, soft bedding and use of car seats for sleep. In addition, mental illness in either parent was associated with a higher risk for SIDS. A new study suggests there may be a genetic component to SIDs and SUDC.

Study Synopsis and Perspective

Researchers have identified pathogenic gene variations in 12% of cases of SUDC.

The new study, which involved 116 cases of SIDS or SUDC, suggests that available methods of chromosome testing could be used to help screen for the conditions, which together account for roughly 1800 fatalities a year in the United States.

“Even though the Back to Sleep campaign has been incredibly effective and safe sleep practices have been promoted for years, sudden unexplained death in pediatrics remains a leading cause of death for infants and children,” said Catherine Brownstein, MPH, PhD, from Boston Children’s Hospital in Massachusetts, lead author of the new study.^[2]

The findings suggest that chromosomal microarray analysis (CMA), the method that the researchers used in the study, “should be considered in the genetic evaluation of SUDC,” Dr Brownstein said. The approach is the first-line method of identifying conditions such as autism spectrum disorder (ASD), developmental disabilities, multiple congenital anomalies, and epilepsy, she noted.

In the study, published in Advanced Genetics, Dr Brownstein and colleagues used CMA to test genes from 116 deceased infants and toddlers up to age 28 months whose deaths were classified as SIDS or SUDC (the latter term applies to children older than 1 year).

The average age at the time of death was 5.7 months; 59% of the patients were boys. In 14 of the children (12%), the CMA test identified genetic variations in the form of deletions or duplications that were pathogenic (5 cases) or uncertain but “favoring pathogenicity” (9 cases). Such deletions or duplications are known as copy number variants (CNVs).

CNVs are present in most people and are not necessarily associated with disease, according to the researchers. However, certain CNVs have been linked to ASD, attention-deficit/hyperactivity disorder, schizophrenia, Crohn’s disease, epilepsy, and various congenital abnormalities.

Dr Brownstein’s group also compared pathogenicity in the SUDC group with that of a cohort of children with ASD and with healthy control persons. They found no significant difference in pathogenicity between SUDC and autism with regard to duplications. However, children in the SUDC group were significantly more likely to have higher pathogenicity scores for deletions compared with control persons. Some of the CMVs did not appear connected to SIDS or SUDC; 2 cases in boys were undiagnosed cases of Klinefelter syndrome.

The study findings were limited by several factors, including the small sample size and the inability to conduct CMA analyses on parents or obtain family history, the researchers note. Other limitations were that phenotypic data were available only from autopsy material and medical records and that the study focused on younger children, the researchers add. They did not speculate about the causes of deaths in the other cases that they examined.

Findings Support Clinical Value of CMA

In the current study, the other 88% of cases could involve nongenetic factors or genetic factors that are not measured by next-generation sequencing or chromosomal microarray, Dr Brownstein said. “Undiagnosed disease programs looking for genetic causes for diseases in living patients identify a cause in about 1 in 4 cases,” she said. “While 12% is a modest percentage, the CNVs identified provide additional information. In the future, the goal would be to capture the full range of potential genetic changes.”

Previous research by Dr Brownstein’s group at Robert’s Program, a clinical service for SUDC families at Boston Children’s Hospital, found genetic variants that might cause sudden death in children.

“We began this study with the simple question of whether, as a population, these children carry more copy number variation, which they do,” she said. “However, none of the CMA findings we identified are currently associated with SUDC, so much more investigation is necessary to find out if they are coincidental, risk factors, or causative.”

Looking ahead, she said, “Ideally, we would want every family affected by sudden unexplained death in pediatrics to have genetic testing, including a chromosomal microarray. Once we have more families enrolled and tested, we will be able to understand the risk factors for SIDS and SUDC much better.”

Benjamin Solomon, MD, clinical director at the National Human Genome Research Institute, said that the new research “may bring answers for individual situations, as well as enable research to understand the overall biological underpinnings and causes of disease.”

The findings “help reinforce the heterogeneous nature of SUDC and related conditions,” Dr Solomon said. “The results also highlight some of the challenges regarding how to interpret the possible clinical effects of genetic changes. That is, every person has genetic changes, and interpreting how certain genetic changes may or may not contribute to a disease or healthcare outcome can be challenging.”

Research is needed to understand not only the overall causes of SUDC but also how the different causes interact, Dr Solomon said. “Eventually, better understanding of the causes could lead to knowledge that would enable interventions that could help prevent or reduce these devastating outcomes.”

The study was supported by the Robert’s Program on Sudden Unexplained Death in Pediatrics, the Jude Zayac Foundation, multiple grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development/National Institutes of Health, the Boston Children’s Hospital Intellectual and the Developmental Disabilities Research Center Molecular Genetics Core Facility (supported by the National Institutes of Health/Eunice Kennedy Shriver National Institute of Child Health and Human Development), and the National Institute of Mental Health/National Institutes of Health. The researchers and Dr Solomon have disclosed no relevant financial relationships.

Adv Genet. Published online November 7, 2022.

Clinical Implications

• Although the rate of SIDS in the US has declined in the past several decades, the prevalence of SIDS remains approximately twice as high among Black and American Indian/Alaska Native populations. The most important risk factors for SIDS involve the sleep environment. The use of car seats for sleep and soft bedding materials also increases the risk for SIDS. Mental illness in either parent is associated with a higher risk for SIDS.
• 4.3% of SUDP cases in the current study had a CNV categorized as pathogenic or likely pathogenic and linked to a known disease. These CNVs were associated with a number of neuropsychological disorders, including autism spectrum disorder, schizophrenia, spinal muscular atrophy, and deafness. The odds ratio for pathological CNVs in comparing cases of SUDP with healthy controls was 1.24.
• Implications for the healthcare team: When counseling parents regarding the risk for SUDP, the healthcare team should consider family history and possible genetic implications.

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