Reassessing the Value of CSF Protein and Glucose Measurement in Pediatric Infectious Meningitis.

OBJECTIVES: Infectious meningitis (IM) in US children is increasingly rare and new rapid multiplex PCR-based testing is increasingly available. We evaluated the added value of cerebrospinal fluid (CSF) protein and glucose tests to predict IM when compared with information provided by CSF white blood cell count (WBC) and multiplex polymerase chain reaction (PCR). METHODS: We retrospectively reviewed CSF results from October 2015 to August 2017 in patients 0 to 18 years at a US children's hospital. Noninfectious evaluations were excluded. Test characteristics were calculated for CSF WBC, protein, and glucose in isolation and in parallel for prediction of microbiologically confirmed IM. Chart review was performed to identify consideration of protein and glucose in medical decision-making (MDM). RESULTS: We identified 735 patients including 446 <2 months; 45 (6.1%) had microbiologically-confirmed IM, including 23 (5.2%) age <2 months. Multiplex PCR and/or CSF WBC identified all IM patients. When added to CSF WBC, measurement of glucose made no contribution to sensitivity, specificity, positive predictive value (PPV) or negative predictive value (NPV), and protein had no impact on sensitivity and decreased the specificity, PPV, and NPV compared with CSF WBC alone. Abnormal protein was documented in MDM in 6 (0.8%) patients, all of whom had elevated WBC counts also cited. Glucose was not mentioned in MDM. CONCLUSIONS: Multiplex PCR testing and WBC may be sufficient to predict meningitis in children in low incidence settings. Protein and glucose did not contribute significant additional information. More intentional use of protein and glucose testing in patients with suspected IM may achieve higher value care.

Genetic architecture of a body colour cline in Drosophila americana.

Phenotypic variation within a species is often structured geographically in clines. In Drosophila americana, a longitudinal cline for body colour exists within North America that appears to be due to local adaptation. The tan and ebony genes have been hypothesized to contribute to this cline, with alleles of both genes that lighten body colour found in D. americana. These alleles are similar in sequence and function to the allele fixed in D. americana's more lightly pigmented sister species, Drosophila novamexicana. Here, we examine the frequency and geographic distribution of these D. novamexicana-like alleles in D. americana. Among alleles from over 100 strains of D. americana isolated from 21 geographic locations, we failed to identify additional alleles of tan or ebony with as much sequence similarity to D. novamexicana as the D. novamexicana-like alleles previously described. However, using genetic analysis of 51 D. americana strains derived from 20 geographic locations, we identified one new allele of ebony and one new allele of tan segregating in D. americana that are functionally equivalent to the D. novamexicana allele. An additional 5 alleles of tan also showed marginal evidence of functional similarity. Given the rarity of these alleles, however, we conclude that they are unlikely to be driving the pigmentation cline. Indeed, phenotypic distributions of the 51 backcross populations analysed indicate a more complex genetic architecture, with diversity in the number and effects of loci altering pigmentation observed both within and among populations of D. americana. This genetic heterogeneity poses a challenge to association studies and genomic scans for clinal variation, but might be common in natural populations.

The ontogeny of color: developmental origins of divergent pigmentation in Drosophila americana and D. novamexicana.

Pigmentation is a model trait for evolutionary and developmental analysis that is particularly amenable to molecular investigation in the genus Drosophila. To better understand how this phenotype evolves, we examined divergent pigmentation and gene expression over developmental time in the dark-bodied D. americana and its light-bodied sister species D. novamexicana. Prior genetic analysis implicated two enzyme-encoding genes, tan and ebony, in pigmentation divergence between these species, but questions remain about the underlying molecular mechanisms. Here, we describe stages of pupal development in both species and use this staging to determine when pigmentation develops and diverges between D. americana and D. novamexicana. For the developmental stages encompassing pigment divergence, we compare mRNA expression of tan and ebony over time and between species. Finally, we use allele-specific expression assays to determine whether interspecific differences in mRNA abundance have a cis-regulatory basis and find evidence of cis-regulatory divergence for both tan and ebony. cis-regulatory divergence affecting tan had a small effect on mRNA abundance and was limited to a few developmental stages, yet previous data suggests that this divergence is likely to be biologically meaningful. Our study suggests that small and developmentally transient expression changes may contribute to phenotypic diversification more often than commonly appreciated. Recognizing the potential phenotypic impact of such changes is important for a scientific community increasingly focused on dissecting quantitative variation, but detecting these types of changes will be a major challenge to elucidating the molecular basis of complex traits.