Of mice and children: Reminiscences of a teratogeneticist

Gene-environment interactions: aligning birth defects research with complex etiology

Developmental biologists rely on genetics-based approaches to understand the origins of congenital abnormalities. Recent advancements in genomics have made it easier than ever to investigate the relationship between genes and disease. However, nonsyndromic birth defects often exhibit non-Mendelian inheritance, incomplete penetrance or variable expressivity. The discordance between genotype and phenotype indicates that extrinsic factors frequently impact the severity of genetic disorders and vice versa. Overlooking gene-environment interactions in birth defect etiology limits our ability to identify and eliminate avoidable risks. We present mouse models of sonic hedgehog signaling and craniofacial malformations to illustrate both the importance of and current challenges in resolving gene-environment interactions in birth defects. We then prescribe approaches for overcoming these challenges, including use of genetically tractable and environmentally responsive in vitro systems. Combining emerging technologies with molecular genetics and traditional animal models promises to advance our understanding of birth defect etiology and improve the identification and protection of vulnerable populations.

How diseases became "genetic"

This article examines the origins of the term "genetic disease." In the late 19 and early 20th century, an earlier idea that diseases that occur in families reflect a vague familiar "predisposition" was replaced by the view that such diseases have specific causes, while Mendelian genetics provided then clues to the patterns of their transmission. The genetictisation of inborn pathologies took a decisive turn with the redefinition, in 1959, of Down syndrome as a chromosomal anomaly, then the development of tests for the diagnosis of other hereditary pathologies. At that time, geneticists distinguished "hereditary" diseases that run in families, from "genetic" conditions that are the result of new mutations during the production of egg and sperm cells. In the latter case, the inborn impairment is produced by an anomaly in the genetic material of the cell, but is not hereditary, because it is not transmitted from one or both parents. In the late 20th and early 21st century, new genomic technologies blurred the distinction between hereditary and genetic impairments, extended the concept of genetic disease, and modified the experience of people living with such a disease.

Understanding chondrodysplasia (cho): A comprehensive review of cho as an animal model of birth defects, disorders, and molecular mechanisms

BACKGROUND

The mutant chondrodysplasia (cho) is a cartilage-targeting disorder in C57BL mice that results in dwarfing and other malformations stemming from this collagenopathy. Clarke Fraser made the discovery of the mutation accidentally in the early 1960s during the thalidomide tragedy.

METHODS

For this review we identified key research on cho as since its discovery. Relevant data were compiled to make a comprehensive review that details discoveries associated with the cho mutation, that describes the associated phenotypes and molecular mechanisms, and that provides a discussion surrounding its current clinical relevance.

RESULTS

Mechanistically, cho acts by hindering chondrogenesis and endochondral bone formation. The phenotype results from a 1-nt deletion in the gene encoding the alpha 1 chain of type XI collagen. For more than half a century, researchers have studied the pathogenesis of the cho mutation in relation to a variety of mouse models of human birth defects and disease. These studies have resulted in several discoveries linking cho with such human disorders as dwarfism, tracheal stenosis, cleft palate, pulmonary hypoplasia, and osteoarthritis (OA).

CONCLUSION

The study of cho has led to numerous advances in understanding human birth defects, congenital disorders, and adult human disease. The most recent studies have suggested a role for the TGF-Beta, HtrA1, Ddr2, and Mmp-13 pathway in the degradation of articular cartilage and the development of OA in cho/+ mice. We have shown that the anti-hypertension drug Losartan is a TGF-Beta blocker that could be used to treat OA in Stickler syndrome, and thereby rescue the WT phenotype.

How genetics came to the unborn: 1960-2000

Prenatal diagnosis (PND) is frequently identified with genetic testing. The termination of pregnancy for foetal malformation was called 'genetic abortion', in spite of the fact that in many cases the malformation does not result from changes in the genetic material of the cell. This study argues that the 'geneticization' of PND reflected the transformation of the meaning of the term 'genetics' in the 1960s and 70s. Such transformation was linked with the definition of Down syndrome as a genetic condition, and to the key role of search for this condition in the transformation of PND into a routine approach. The identification of PND with the polysemic term 'genetics' was also favoured by hopes that cytogenetic studies will lead to cures or prevention of common birth defects, the association of genetic counsellors with prenatal diagnosis, and the raising prestige of clinical genetics. In spite of the impressive achievements of the latter specialty, more than fifty years after the first prenatal diagnoses, the main 'cure' of a severe foetal malformation remains the same as it was in the 1960s: the termination of a pregnancy. The identification of PND with genetics deflects attention from the gap between scientists' capacity to elucidate the causes of numerous birth defects and their ability (as for now) to prevent or treat these defects, and favours the maintenance of a powerful regimen of hope.