This is an insightful reconstruction of the history of medical genetics, where chromosomes as concepts and images retained their own conceptual and explanatory powers throughout the second half of the twentieth century. The book is composed of a set of episodes, each of them dealing with a genetic disorder whose diagnosis included techniques, instruments and ways of looking at the genome. It moves from the immediate post-war idealised, schematic images and rough microphotographs of chromosomes via DNA fluorescence in situ hybridisation (FISH) to the subsequent molecular ‘gaze’. Naming styles and classifications suggesting an objectivity that molecules, or pieces of them, were expected to provide, participated in a long history of laboratory techniques and the clinical concepts associated with them. Andrew Hogan keeps a careful eye on the clinical and anatomical meaning of the successive concepts. Pieces of the genome are recognised in his narrative as the molecular side of a set of malformation patterns associated with muscular weakness, obesity, small genitals and intellectual development disorders, which are involved in the definition and diagnosis of Prader–Willi syndrome, one of the disorders whose history is scrutinised. The history he recounts is that of a transnational set of disorders, an increasingly promising clinical space built upon a technologised practice of looking at malformations and disorders, the designs and methods of which took part in the emergence of the genetic platform – to use the term that Keating and Cambrosio have coined for this complex set of practices. Inspired by the views, texts and statements of the well-known United States geneticist Victor McKusick, Hogan follows both the clinic and the cytogenetics laboratory and later the molecular genetics laboratory by introducing patients’ perceptions. And even with such a constellation of agencies and frameworks, the reconstruction works perfectly well. From anatomical traits and scientific inquiry to clinical purposes, the routes taken led to an issue that comes back again and again: the fact that treatment and prevention turned out to be unlikely participants in a story centred on the diagnostic powers of twentieth-century medical genetics.

In the introduction the author presents the issue of the relationship between prenatal diagnosis – the author’s confessed early interest when beginning this research – and medical genetics and eugenics. He summarises the main themes tackled, namely genetic syndromes and bodily malformations as clinical and laboratory issues. The first chapter focuses on the organisational aspects of early medical genetics by focusing on the reconstruction of the intellectual disability called X-fragile syndrome. Such a disorder allows the author to show that medical genetics provided diagnostic methods, but treatment was ‘to be understood as a secondary aim’. In the second chapter, Hogan introduces the trajectory taken by chromosome representations by elucidating the techniques that allowed cytogenetics to make human chromosomes visible. The capacities of such images, however limited, allowed the classification of disorders on chromosomal bases and thus provided a reference for detecting anomalies at the very origins of human gene mapping. Chapter 3 is dedicated to Prader–Willi syndrome and the paths toward an increasingly higher-resolution cytogenetic analysis, which in his words ‘never provided the level of enhanced vision its promoters had predicted’. The fourth chapter deals with the introduction of experts and tools from molecular biology in the 1980s, when, during the intense research into recombinant DNA, molecules were envisioned as replacing chromosomes by combining the use of the microscope for chromosome analysis with molecular approaches, thus producing, according to Hogan, the hybrid technique that molecular cytogenetics became. Chapter 5 focuses on the convergent histories of two syndromes that came to be understood as the same condition: DiGeorge and velo-cardio-facial (VCF) syndromes. They were identified as a deletion of the same piece of chromosome 22, named as 22q11. While debates on the names given to these syndromes kept disputes about styles of knowing and the exhibition of authority alive, centres and websites emerged that contributed to institutionalising both their molecular names, and the names of the experts that dealt with them. Chapter 6 beautifully analyses another convergence: between the human genome as an almost endless chain of nucleotides, and the FISH technology that connected them and finally preserved the banding chromosomes as a useful representation of the whole picture. This was useful for patients, clinicians and geneticists alike.

The history of genetic mapping develops as successive techniques were invented. The text is full of suggestive rhetorical and conceptual terms, which explain in a very precise manner how the laboratory bench came to have epistemological superiority over the clinical gaze. The narration effectively accounts for the advances in diagnosis that created the genetic culture of our time and its repositories. The history of medical genetics is presented in detail as a space composed of experimental knowledge and clinical practices that has never fulfilled its promise, but still went beyond scientists’ expectations. The arguments are convincing, and the combined scholarship in history, sociology and medical genetics itself makes such a complex trajectory fully understood.