A s the head of student government at Duke University School of Medicine in Durham, North Carolina, Sujay Kansagra had witnessed several of his fellow students dealing with depression. "I knew

We used non-invasive high frequency ultrasound to screen N-ethyl-N-nitrosourea mutagenized mouse fetuses for congenital cardiovascular anomalies. We ultrasound scanned 7546 mouse fetuses from 262 mutagenized families, and identified 124 families with cardiovascular defects. Represented were most of the major congenital cardiovascular anomalies seen clinically. The ENU-induced mutations in several families were mapped using polymorphic microsatellite DNA markers. One family with forelimb anomalies and ventricular septal defects, phenotypes similar to Holt-Oram syndrome, and one family with transposition of the great arteries and heart situs anomalies were mapped to different regions of mouse chromosome 4. A third mutation causing persistent truncus arteriosus and craniofacial defects, phenotypes reminiscent of DiGeorge syndrome, was mapped to mouse chromosome 2. We note that mouse chromosomes 4 and 2 do not contain Tbx5 or Tbx1, genes previously linked to Holt-Oram and DiGeorge syndromes, respectively. In two other families, the ENU-induced mutation was identified – Sema3CL605P was associated with persistent truncus arteriosus with interrupted aortic arch, and the Gja1W45Xconnexin43 mutation caused conotruncal malformation and coronary aneurysms. Although our screen was designed as a recessive screen, a number of the mutations showed cardiovascular phenotypes in both heterozygote and homozygote animals. These studies show the efficacy of ENU mutagenesis and high-throughput ultrasound phenotyping in recovering mutations causing a wide spectrum of congenital heart defects. These ENU-induced mutations hold promise in yielding new insights into the genetic basis for human congenital heart disease.

No abstract

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder associated with ciliary defects and situs inversus totalis, the complete mirror image reversal of internal organ situs (positioning). A variable incidence of heterotaxy, or irregular organ situs, also has been reported in PCD patients, but it is not known whether this is elicited by the PCD-causing genetic lesion. We studied a mouse model of PCD with a recessive mutation in Dnahc5, a dynein gene commonly mutated in PCD. Analysis of homozygous mutant embryos from 18 litters yielded 25% with normal organ situs, 35% with situs inversus totalis, and 40% with heterotaxy. Embryos with heterotaxy had complex structural heart defects that included discordant atrioventricular and ventricular outflow situs and atrial/pulmonary isomerisms. Variable combinations of a distinct set of cardiovascular anomalies were observed, including superior-inferior ventricles, great artery alignment defects, and interrupted inferior vena cava with azygos continuation. The surprisingly high incidence of heterotaxy led us to evaluate the diagnosis of PCD. PCD was confirmed by EM, which revealed missing outer dynein arms in the respiratory cilia. Ciliary dyskinesia was observed by videomicroscopy. These findings show that Dnahc5 is required for the specification of left-right asymmetry and suggest that the PCD-causing Dnahc5 mutation may also be associated with heterotaxy.