Peripheral blood leukocyte gene expression patterns and metabolic parameters in habitually snoring and non-snoring children with normal polysomnographic findings

Abstract

Background: Children who snore but do not have gas exchange abnormalities or alterations of sleep architecture have primary snoring (PS). Since increasing evidence suggest that PS may be associated with morbidity, we hypothesized that assessing genome-wide gene expression in peripheral blood leukocytes (PBL) will identify a distinct signature in PS children.

Methods: Children (aged 4-9 years) with and without habitual snoring and a normal PSG were designated as either PS or controls. Whole genome expression profiles of PBL and metabolic parameters in 30 children with PS and 30 age-, gender-, ethnicity-, and BMI-matched controls were compared. Pathway-focused gene network analysis of the PBL transcriptome was performed. Metabolic parameters were measured in an independent follow-up cohort of 98 children (64 PS and 34 controls) to evaluate the computationally derived findings.

Results: PS was not associated with a distinct transcriptional signature in PBL. Exploratory functional network analysis of enriched gene sets identified a number of putative pathways-including those mapping to insulin signaling, adipocyte differentiation, and obesity-with significant alterations in glucose metabolism and insulin sensitivity emerging in the follow-up cohort of children with PS, but no differences in lipid profiles.

Conclusions: PS children do not exhibit global perturbations in their PBL transcriptional response, suggesting that current normative PSG criteria are overall valid. However, subtle differences in functionally coherent pathways involved in glycemic homeostasis were detected and confirmed in a larger independent pediatric cohort indicating that PS may carry increased risk for end-organ morbidity in susceptible children.

Keywords: Snoring; children; inflammation; insulin resistance; sleep apnea.

Figure 1

Principal component analysis of peripheral blood leukocyte gene expression from 55 children with primary snoring (n = 29, cyan) and matched controls (n = 26, magenta). The absence of phenotype-specific clusters implies the lack of a significant global transcriptional perturbation.

Figure 2

Gene expression heatmap of “leading edge” members of enriched gene sets in PBL of children with PS vs. controls. One-dimensional hierarchical clustering of expression values has been performed to better depict distinct transcriptional patterns between the phenotypes.

Figure 3

A wiring diagram depiction of the functional categories enriched between children with PS and controls. The intermodular connections reflect the fact that some genes map to multiple modules, while the line thickness is proportional to the number of shared genes.

Figure 4

Gene product interaction network constructed from gene members mapping to the insulin signaling, adipocyte differentiation and obesity module (see Figure 3). Nodes up-regulated in PS are shown in cyan, and those up-regulated in controls are colored in magenta. Members of the leading edge are highlighted in darker shades. Among the complex interactions, note the relational links between leptin, IGF1R, and IRS1 as discussed in the text. A complete list of gene members is provided in the supplementary Table S2.

Figure 5

Assessment of glycemic homeostasis in an independent follow-up cohort comprised of 64 children with PS and 34 matched Controls. Habitually snoring children were stratified into three groups based on their PSG-derived OAHI (PS1: OAHI < 1/h TST, PS2: OAHI < 1.5/h TST, and PS3: OAHI < /h TST). Note that PS1 and PS2 are subsets of PS3, and PS1 is a subset of PS2. There are persistent alterations in fasting glucose, fasting insulin, and HOMA insulin resistance in children with PS compared to Controls, even in habitual snorers with OAHI < 1 /h TST (PS1). Data presented as mean ± SD, P-values are based on 2-tailed Student t-test with unequal variances.