Global genetic analysis in mice unveils central role for cilia in congenital heart disease.

Congenital heart disease (CHD) is the most prevalent birth defect, affecting nearly 1% of live births; the incidence of CHD is up to tenfold higher in human fetuses. A genetic contribution is strongly suggested by the association of CHD with chromosome abnormalities and high recurrence risk. Here we report findings from a recessive forward genetic screen in fetal mice, showing that cilia and cilia-transduced cell signalling have important roles in the pathogenesis of CHD. The cilium is an evolutionarily conserved organelle projecting from the cell surface with essential roles in diverse cellular processes. Using echocardiography, we ultrasound scanned 87,355 chemically mutagenized C57BL/6J fetal mice and recovered 218 CHD mouse models. Whole-exome sequencing identified 91 recessive CHD mutations in 61 genes. This included 34 cilia-related genes, 16 genes involved in cilia-transduced cell signalling, and 10 genes regulating vesicular trafficking, a pathway important for ciliogenesis and cell signalling. Surprisingly, many CHD genes encoded interacting proteins, suggesting that an interactome protein network may provide a larger genomic context for CHD pathogenesis. These findings provide novel insights into the potential Mendelian genetic contribution to CHD in the fetal population, a segment of the human population not well studied. We note that the pathways identified show overlap with CHD candidate genes recovered in CHD patients, suggesting that they may have relevance to the more complex genetics of CHD overall. These CHD mouse models and >8,000 incidental mutations have been sperm archived, creating a rich public resource for human disease modelling.

A letter signed: the very beginnings of Dalton's atomic theory.

This paper explores the provenance and content of a previously unknown personal letter by John Dalton (1766-1844), which is dated 12 April 1803. It relates to a startling breakthrough in Dalton's research, which pre-dates by five months the earliest date in his laboratory notebook, namely, 6 September 1803. The author acquired the letter about thirty years ago, and now offers it to the public. He makes no attempt to explain how it contributes to--or even changes--our understanding of Dalton, but leaves that privilege to Dalton scholars.

Interrogating congenital heart defects with noninvasive fetal echocardiography in a mouse forward genetic screen.

BACKGROUND: Congenital heart disease (CHD) has a multifactorial pathogenesis, but a genetic contribution is indicated by heritability studies. To investigate the spectrum of CHD with a genetic pathogenesis, we conducted a forward genetic screen in inbred mice using fetal echocardiography to recover mutants with CHD. Mice are ideally suited for these studies given that they have the same four-chamber cardiac anatomy that is the substrate for CHD. METHODS AND RESULTS: Ethylnitrosourea mutagenized mice were ultrasound-interrogated by fetal echocardiography using a clinical ultrasound system, and fetuses suspected to have cardiac abnormalities were further interrogated with an ultrahigh-frequency ultrasound biomicroscopy. Scanning of 46 270 fetuses revealed 1722 with cardiac anomalies, with 27.9% dying prenatally. Most of the structural heart defects can be diagnosed using ultrasound biomicroscopy but not with the clinical ultrasound system. Confirmation with analysis by necropsy and histopathology showed excellent diagnostic capability of ultrasound biomicroscopy for most CHDs. Ventricular septal defect was the most common CHD observed, whereas outflow tract and atrioventricular septal defects were the most prevalent complex CHD. Cardiac/visceral organ situs defects were observed at surprisingly high incidence. The rarest CHD found was hypoplastic left heart syndrome, a phenotype never seen in mice previously. CONCLUSIONS: We developed a high-throughput, 2-tier ultrasound phenotyping strategy for efficient recovery of even rare CHD phenotypes, including the first mouse models of hypoplastic left heart syndrome. Our findings support a genetic pathogenesis for a wide spectrum of CHDs and suggest that the disruption of left-right patterning may play an important role in CHD.