Congenital diseases reveal a lot about human biology

WHEN A CLINICIAN showed Dr Nizar’s sons a pain chart, they asked her what the smiley face at one end of the scale meant. The boys do not know, Dr Nizar says, what it is like to live without pain. Not all the diseases caused by calamitously failed single genes are quite that awful. But unlike the more generalised genomic influences on health—those to which everyone is heir, but few know about—people with serious congenital diseases have no escape or respite; their symptoms are inescapable. And so, too, for the most part, are their diseases. Genomics makes the diagnosis of such diseases, especially the rare ones, easier and more precise, and it has revealed what is going on in some of them in useful ways. It has not yet, though, provided much by way of cures. Now this is beginning to change.