(HealthDay News) – A gene variant on the X-chromosome is associated with sudden infant death syndrome (SIDS) only in boys, particularly those who die at the ages of highest SIDS prevalence, according to a study published online Feb. 20 in Pediatrics.

Noting that the X-chromosomal monoamine oxidase A (MAOA) gene is important in both the serotonergic and noradrenergic neuronal systems, Michael Klintschar, MD, from Medical University Hannover, and Christian Heimbold, from Georg August University Göttingen – both in Germany, examined the frequency of functional polymorphism in the promoter of the MAOA gene in 156 white SIDS cases and 260 gender- and age-matched controls.

The researchers found that the pooled low-expressing alleles *2 and *3 were present in 44.4% of male SIDS cases but only 25.5% of male control cases. In contrast, there were no differences for females. These alleles were more frequent in infants who died at ages of 46–154 days than those who died at an older age (54.9% vs. 22.6%).

“Our results indicate a relationship between SIDS and the MAOA genotype in boys via influencing serotonergic and noradrenergic neurons in the brainstem,” the authors conclude. “This locus is the first X-chromosomal locus associated with SIDS.”

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