Causes of Most Birth Defects Remain Unknown

Nicola M. Parry, DVM

May 30, 2017

The causes of most major birth defects remain unknown, a new study shows.

Marcia L. Feldkamp, PhD, from the University of Utah School of Medicine, Salt Lake City, and colleagues published the results of their study online May 30 in the BMJ.

"In this five year population based birth defect case cohort, systematic clinical review identified known etiology in only one in five — specific etiology could not be conclusively assigned in most (79.8%) cases," the authors write.

In the United States, major birth defects affect one in 33 babies, translating to an estimated annual direct healthcare cost of $2.6 billion. Birth defects are also the leading cause of infant mortality, accounting for one in every five deaths in the United States in the first year of life.

However, although evidence for associations between known risk factors, such as maternal diabetes, and birth defects continues to grow, the exact causes of most of these defects remain unknown.

The researchers therefore aimed to investigate causes of major birth defects in children born from 2005 to 2009, using Utah's population-based surveillance system.

They identified 5504 infants with major birth defects among 270,878 total births (a prevalence of 2.03%).

A known cause was assigned in only 20.2% (1114) of these cases, with chromosomal or genetic conditions accounting for 94.4%, teratogen exposure for 4.1%, and anomalies associated with twinning for 1.4%.

Among the remaining 79.8% (4390) of cases with no known cause, 88.2% were isolated birth defects, and only 4.8% were associated with a documented family history of similar defects.

However, the authors believe that the estimate of 20% of birth defect cases with a known etiology is a conservative one. As genetic technology continues to advance, leading to more discoveries about the genetic causes of birth defects, the proportion of cases with a known cause will rise, they say.

They also note that the etiology of birth defects with no known cause is probably complex, and may involve interactions between genetic profiles and environmental factors before conception and during early gestation.

Nevertheless, the results of this study demonstrate that a specific cause still cannot be determined for most birth defects, highlighting the persistent gaps in knowledge about birth defects and the challenge of preventing them. But, Dr Feldkamp and colleagues stress that these gaps also represent opportunities for both basic and translational researchers. Identifying the cause of these defects is a key step that will help investigators focus research efforts for reducing the risk for birth defects or preventing their occurrence.

"Understanding the etiology of birth defects should be both a public health and research priority," they conclude.

This study was supported by grants from the Centers for Disease Control and Prevention, and the Health Resources and Services Administration of the US Department of Health and Human Services.

The authors have disclosed no relevant financial relationships.

Br Med J. Published online May 30, 2017. Abstract

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