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X-linked genes help explain why boys of all ages face higher respiratory risk

chromosome

A multi-institution research team that includes Children’s National Health System attempted to characterize gender-based epigenomic signatures in the human airway early in children’s lives with a special attention to defining DNA methylation patterns of the X chromosome.

Human airways already demonstrate gender-based differences in DNA methylation signatures at birth, providing an early hint of which infants may be predisposed to develop respiratory disorders like asthma later in life, a research team reports in a paper published online April 3, 2018, in Scientific Reports.

It’s clear that boys and young men are more likely to develop neonatal respiratory distress syndrome, bronchopulmonary dysplasia, viral bronchiolitis, pneumonia, croup and childhood asthma. Unlike boys, girls have an additional copy of the X chromosome, which is enriched with immune-related genes, some of which play key roles in the development of respiratory conditions. Methylation prevents excessive gene activity in X-linked genes, however much remains unknown about how this process influences infants’ risk of developing airway diseases.

A multi-institution research team that includes Children’s National Health System attempted to characterize gender-based epigenomic signatures in the human airway early in children’s lives with a special attention to defining DNA methylation patterns of the X chromosome.

“It’s clear as we round in the neonatal intensive care unit that baby boys remain hospitalized longer than girls and that respiratory ailments are quite common. Our work provides new insights about gender differences in airway disease risk that are pre-determined by genetics,” says Gustavo Nino, M.D., a Children’s pulmonologist and the study’s senior author.

“Characterizing early airway methylation signatures holds the promise of clarifying the nature of gender-based disparities in respiratory disorders and could usher in more personalized diagnostic and therapeutic approaches.”

The research team enrolled 12 newborns and infants in the study and obtained their nasal wash samples. Six of the infants were born preterm, and six were born full term. The researchers developed a robust gender classification algorithm to generate DNA methylation signals. The machine learning algorithm identified X-linked genes with significant differences in methylation patterns in boys, compared with girls.

As a comparison group, they retrieved pediatric nasal airway epithelial cultures from a study that looked at genomic DNA methylation patterns and gene expression in 36 children with persistent atopic asthma compared with 36 heathy children.

The team went on to classify X-linked genes that had significant gender-based X methylation and those genes whose X methylation was variable.

“These results confirm that the X chromosome contains crucial information about gender-related genetic differences in different airway tissues,” Dr. Nino says. “More detailed knowledge of the genetic basis for gender differences in the respiratory system may help to predict, prevent and treat respiratory disorders that can affect patients over their entire lifetimes.”

In addition to Dr. Nino, study co-authors include Lead Author Cesar L. Nino, bioinformatics scientist, Pontificia Universidad Javeriana; Geovanny F. Perez, M.D., co-director of Children’s Severe Bronchopulmonary Dysplasia Program; Natalia Isaza Brando, M.D., Children’s neonatology attending; Maria J. Gutierrez, Johns Hopkins University School of Medicine; and Jose L. Gomez, Yale University School of Medicine.

Financial support for this research was provided by the National Institutes of Health under award numbers
AI130502-01A1, HL090020, HL125474-03, HD001399, UL1TR000075 and KL2TR000076.

Human Rhinovirus

When a common cold may trigger early supportive care

Human Rhinovirus

A new study led by Children’s National Health System shows that in infants who were born severely premature, human rhinovirus infections appear to trigger airway hyper-reactivity, which leads to wheezing, hyperinflation and more severe respiratory disease.

Human rhinovirus (HRV), the culprit behind most colds, is the leading cause of hospitalization for premature babies. However, in very preterm children, exactly how HRV causes severe respiratory disease – and which patients may need more intensive observation and treatment – is less well understood.

A new study led by Children’s National Health System research-clinicians showed in children who were born severely premature, HRV infections seem to trigger an airway hyper-reactivity (AHR) type of disease, which leads to wheezing and air-trapping (hyperinflation) and more severe respiratory disease. This, in turn, increases the risk for hospitalization.

The study, published online Oct. 21, 2017 in Pediatrics and Neonatology, found that other signs of respiratory distress, such as low arterial blood oxygen or rapid shallow breathing, were no more common in severely premature children (less than 32 weeks of gestational age) than in kids born preterm or full-term. The findings have implications for administering supportive care sooner or more intensively for severely premature children than for other infants.

“When it comes to how they respond to such infections, severely premature children are quite different,” says Geovanny Perez, M.D., a specialist in pulmonary medicine at Children’s National and lead study author. “We’ve known they are more susceptible to human rhinovirus infection and have more severe disease. However, our study findings suggest that severely premature kids have an ‘asthma’ type of clinical picture and perhaps should be treated differently.”

The study team sought to identify clinical phenotypes of HRV infections in young children hospitalized for such infections. The team theorized that severely premature babies would respond differently to these infections and that their response might resemble symptoms experienced by patients with asthma.

“For a number of years, our team has studied responses to viruses and prematurity, especially HRV and asthma,” Dr. Perez says. “We know that premature babies have an immune response to HRV from the epithelial cells, similar to that seen in older patients with asthma. But we wanted to address a gap in the research to better understand which children may need closer monitoring and more supportive care during their first HRV infection.”

Geovanny Perez

“When it comes to how they respond to such infections, severely premature children are quite different,” says Geovanny Perez, M.D. “We’ve known they are more susceptible to human rhinovirus infection and have more severe disease. However, our study findings suggest that severely premature kids have an ‘asthma’ type of clinical picture and perhaps should be treated differently.”

In a retrospective cross-sectional analysis, the study looked at 205 children aged 3 years or younger who were hospitalized at Children’s National in 2014 with confirmed HRV infections. Of these, 71 percent were born full-term (more than 37 gestational weeks), 10 percent were preterm (32 to 37 gestational weeks) and 19 percent were severely premature (less than 32 gestational weeks).

Dr. Perez and his team developed a special respiratory distress scoring system based on physical findings in the children’s electronic medical records to assess the degree of lower-airway obstruction or AHR (as occurs in asthma) and of parenchymal lung disease. The physical findings included:

  • Wheezing;
  • Subcostal retraction (a sign of air-trapping/hyperinflation of the lungs), as can occur in pneumonia;
  • Reduced oxygen levels (hypoxemia); and
  • Increased respiratory rate (tachypnea).

The research team assigned each case an overall score. The severely premature children had worse overall scores – and significantly worse scores for AHR and hyperinflated lungs relative to children born late preterm or full-term.

“What surprised us, though, in this study was that the phenotypical characterization using individual parameters for parenchymal lung disease, such as hypoxemia or tachypnea, were not different in severe preterm children and preterm or full term,” says Dr. Perez. “On the other hand, our study found that severely preterm children had a lower airway obstruction phenotype associated with retractions and wheezing. Moreover there was a ‘dose effect’ of prematurity: Children who were born more premature had a higher risk of wheezing and retractions.”

Among the implications of this study, Dr. Perez sees the potential to use phenotypical (clinical markers, such as retractions and wheezing) and biological biomarkers to better personalize patients’ treatments. Dr. Perez and his team have identified biological biomarkers in nasal secretions of children with rhinovirus infection that they plan to combine with clinical biomarkers to identify which patients with viral infections will benefit from early supportive care, chronic treatments or long-term monitoring.

Dr. Perez says further research in this area should pursue a number of paths, including:

  • A longitudinal study to elucidate which children will benefit from asthma-like treatment, such as bronchodilators or corticosteroids;
  • A study of biomarkers, including microRNAs and other inflammatory molecules; or
  • Alternatively, a longitudinal study exploring the mechanism by which wheezing develops, perhaps looking at first and subsequent rhinovirus infections in babies born at different gestational ages.