Advances and challenges in genetic technologies to produce single-sex litters.

There is currently a requirement for single-sex litters for many applications, including agriculture, pest control, and reducing animal culling in line with the 3Rs principles: Reduction, Replacement, and Refinement. The advent of CRISPR/Cas9 genome editing presents a new opportunity with which to potentially generate all-female or all-male litters. We review some of the historical nongenetic strategies employed to generate single-sex litters and investigate how genetic and genome editing techniques are currently being used to produce all-male or all-female progeny. Lastly, we speculate on future technologies for generating single-sex litters and the possible associated challenges.

Clinical consensus document for fitting non-surgical transcutaneous bone conduction hearing devices to children.

This clinical consensus document addresses the assessment, selection, and fitting considerations for non-surgical bone conduction hearing devices (BCHD) for children under the age of 5 years identified as having unilateral or bilateral, permanent conductive or mixed hearing losses. Children with profound unilateral sensorineural hearing losses are not addressed. The document was developed based on evidence review and consensus by The Paediatric Bone Conduction Working Group, which is composed of audiologists from North America who have experience working with BCHDs in children. The document aims to provide clinical direction for an area of paediatric audiology practice that is under development and is therefore lacking in standard protocols or guidelines. This work may serve as a basis for future research and clinical contributions to support prospective paediatric audiology practices.

Prevalence of Childhood Permanent Hearing Loss after Early Complex Cardiac Surgery.

OBJECTIVES: To estimate the prevalence of childhood permanent hearing loss (PHL) after early cardiac surgery. STUDY DESIGN: This prospective observational (1996-2015) study after complex cardiac surgery with cardiopulmonary bypass at ≤6 weeks of life reports audiology follow-up by registered pediatric-experienced audiologists at 6-8 months postsurgery, age 2 years, and as required throughout and thereafter to complete diagnoses. PHL at any frequency (500-4000 Hz) is defined as responses of >25-decibel hearing level in either ear. PHL was evaluated by type (conductive or sensorineural), pattern (flat or sloping), and severity (mild to profound). RESULTS: Survival rate was 83.4% (706 of 841 children) with a 97.9% follow-up rate (691 children); 41 children had PHL, 5.9% (95% CI 4.3%, 8.0%). By cardiac defect, prevalence was biventricular, 4.0% (95%CI 2.5%, 6.1%); single ventricle, 10.8% (95%CI 6.8%, 16.1%). Eighty-seven (12.6%) of 691 had syndromes/genetic abnormalities with known association with PHL; of these, 17 (41.5%) had PHL. Of 41 children, 4 had permanent conductive, moderate to severe loss (1 bilateral); 37 had moderate to profound sensorineural loss (29 bilateral with 20 sloping and 9 flat), 6 with cochlear implant done or recommended. CONCLUSIONS: Infants surviving complex cardiac surgery are at high risk for PHL. Over 40% with PHL have known syndromes/genetic abnormalities, but others do not have easily identifiable risk indicators. Early cardiac surgery should be considered a risk indicator for PHL.

CRISPR-Cas9 effectors facilitate generation of single-sex litters and sex-specific phenotypes.

Animals are essential genetic tools in scientific research and global resources in agriculture. In both arenas, a single sex is often required in surplus. The ethical and financial burden of producing and culling animals of the undesired sex is considerable. Using the mouse as a model, we develop a synthetic lethal, bicomponent CRISPR-Cas9 strategy that produces male- or female-only litters with one hundred percent efficiency. Strikingly, we observe a degree of litter size compensation relative to control matings, indicating that our system has the potential to increase the yield of the desired sex in comparison to standard breeding designs. The bicomponent system can also be repurposed to generate postnatal sex-specific phenotypes. Our approach, harnessing the technological applications of CRISPR-Cas9, may be applicable to other vertebrate species, and provides strides towards ethical improvements for laboratory research and agriculture.

Genetic dissection of Down syndrome-associated congenital heart defects using a new mouse mapping panel.

Down syndrome (DS), caused by trisomy of human chromosome 21 (Hsa21), is the most common cause of congenital heart defects (CHD), yet the genetic and mechanistic causes of these defects remain unknown. To identify dosage-sensitive genes that cause DS phenotypes, including CHD, we used chromosome engineering to generate a mapping panel of 7 mouse strains with partial trisomies of regions of mouse chromosome 16 orthologous to Hsa21. Using high-resolution episcopic microscopy and three-dimensional modeling we show that these strains accurately model DS CHD. Systematic analysis of the 7 strains identified a minimal critical region sufficient to cause CHD when present in 3 copies, and showed that it contained at least two dosage-sensitive loci. Furthermore, two of these new strains model a specific subtype of atrio-ventricular septal defects with exclusive ventricular shunting and demonstrate that, contrary to current hypotheses, these CHD are not due to failure in formation of the dorsal mesenchymal protrusion.

Down syndrome is a condition caused by having an extra copy of one of the 46 chromosomes found inside human cells. Specifically, instead of two copies, people with Down syndrome are born with three copies of chromosome 21. This results in many different effects, including learning and memory problems, heart defects and Alzheimer's disease. Each of these different effects is caused by having a third copy of one or more of the approximately 230 genes found on chromosome 21. However, it is not known which of these genes cause any of these effects, and how an extra copy of the genes results in such changes. Now, Lana-Elola et al. have investigated which genes on chromosome 21 cause the heart defects seen in Down syndrome, and how those heart defects come about. This involved engineering a new strain of mouse that has an extra copy of 148 mouse genes that are very similar to 148 genes found on chromosome 21 in humans. Like people with Down syndrome, this mouse strain developed heart defects when it was an embryo. Using a series of six further mouse strains, Lana-Elola et al. then narrowed down the potential genes that, when in three copies, are needed to cause the heart defects, to a list of just 39 genes. Further experiments then showed that at least two genes within these 39 genes were required in three copies to cause the heart defects. The next step will be to identify the specific genes that actually cause the heart defects, and then work out how a third copy of these genes causes the developmental problems.