Preventing False Safety by Introducing the Hygienic Air Delivery Rate (HADR) for Mobile Air Purifiers

Indoor environments can become contaminated with pathogen-laden respiratory droplets exhaled by people, posing a risk of infection to others. To address this issue, indoor spaces are typically cleaned by ventilating-bringing in fresh outside air and expelling contaminated air. Mobile air purifiers can also help mitigate this risk and are widely used, particularly during emergent situations such as pandemics. However, a thorough assessment of how to measure the effective cleaning performance of air purifiers is still needed. Currently, the clean air delivery rate (CADR) is used as a standard metric to evaluate air purifiers. In this protocol, however, we identify steps that may erroneously influence the measured cleaning rate, potentially leading to falsely safe estimates. To address this, we propose a modified protocol to estimate the hygienic air delivery rate (HADR), which more accurately reflects the effective cleaning performance of air purifiers. We also suggest several considerations to enhance the HADR effectiveness of these devices. Additionally, we present case studies of real devices demonstrating that the HADR can be significantly lower than the volume flow rate of the air purifiers. We emphasize that the HADR-rather than the volume flow rate-should be used by both manufacturers and consumers to evaluate and compare devices, in order to prevent a false sense of safety

De novo mutations in SMCHD1 cause Bosma arhinia microphthalmia syndrome and abrogate nasal development

Bosma arhinia microphthalmia syndrome (BAMS) is an extremely rare and striking condition characterized by complete absence of the nose with or without ocular defects. We report here that missense mutations in the epigenetic regulator SMCHD1 mapping to the extended ATPase domain of the encoded protein cause BAMS in all 14 cases studied. All mutations were de novo where parental DNA was available. Biochemical tests and in vivo assays in Xenopus laevis embryos suggest that these mutations may behave as gain-of-function alleles. This finding is in contrast to the loss-of-function mutations in SMCHD1 that have been associated with facioscapulohumeral muscular dystrophy (FSHD) type 2. Our results establish SMCHD1 as a key player in nasal development and provide biochemical insight into its enzymatic function that may be exploited for development of therapeutics for FSHD

An endogenous small interfering RNA pathway in Drosophila

Drosophila endogenous small RNAs are categorized according to their mechanisms of biogenesis and the Argonaute protein to which they bind. MicroRNAs are a class of ubiquitously expressed RNAs of 22 nucleotides in length, which arise from structured precursors through the action of Drosha - Pasha and Dicer- 1-Loquacious complexes(1-7). These join Argonaute-1 to regulate gene expression(8,9). A second endogenous small RNA class, the Piwi-interacting RNAs, bind Piwi proteins and suppress transposons(10,11). Piwi- interacting RNAs are restricted to the gonad, and at least a subset of these arises by Piwi- catalysed cleavage of single-stranded RNAs12,13. Here we show that Drosophila generates a third small RNA class, endogenous small interfering RNAs, in both gonadal and somatic tissues. Production of these RNAs requires Dicer- 2, but a subset depends preferentially on Loquacious(1,4,5) rather than the canonical Dicer- 2 partner, R2D2 ( ref. 14). Endogenous small interfering RNAs arise both from convergent transcription units and from structured genomic loci in a tissue- specific fashion. They predominantly join Argonaute- 2 and have the capacity, as a class, to target both protein- coding genes and mobile elements. These observations expand the repertoire of small RNAs in Drosophila, adding a class that blurs distinctions based on known biogenesis mechanisms and functional roles