You’ve probably come across the name Kary Mullis recently, via social media. He’s best remembered for his invention (along with a team of other researchers) of the Polymerase Chain Reaction, or PCR for short (and for many biology students was probably immortalised in their memories via this earworm of an advertisement¹).
This turned out to be a very powerful tool, often used in combination with genome sequencing, for medical researchers and other scientists. It’s been used for everything from determining paternity, forensic testing, ancient DNA (aDNA) work on human ancestors (and other species), obtaining enough DNA from a specific gene for research on genetic disorders, and more besides, including identifying the presence of SARS-Cov-2. If you’d like to learn more about the technique, there’s a good explanation here, and teachers might find this video by the Amoeba Sisters useful with their classes.
Mullis & his colleagues² patented the invention in 1985, and in 1993 he received the Nobel Prize for his work.
Now, I’ve mentioned the patent quite deliberately, because I’ve seen it claimed that Mullis said PCR could not be used to identify the presence of particular pathogens. So, here’s a link to the patent, which states – in the first sentence of the abstract – that the invention (PCR) is a process for amplifying and detecting any target nucleic acid sequence. This is expanded on page 14 of the document: the technique is for amplifying existing nucleic acid sequences if they are present in a test sample and detecting them if present using a probe. And then, on page 22:
The method herein may also be used to enable detection and/or characterisation of specific nucleic acid sequences associated with infections diseases.
And on the following page:
Various infectious diseases can be diagnosed by the presence in clinical samples of specific DNA sequences characteristic of the causative microorganism [including bacteria, viruses, and parasites] … Specific amplification of suspected sequences … could greatly improve the sensitivity and specificity of these [existing] procedures.
It’s absolutely clear from this document that Mullis and his fellow researchers/inventors intended the technology to be used to detect the presence of pathogens that cause infectious diseases.
So, where has the confusion come from?
Well, sadly, by 1995 Mullis had become something of a scientific contrarian: he argued that the Human Immunodeficiency Virus (HIV) was not the cause of AIDS, an idea he mentions in his autobiography (Dancing Naked in the Mind Fields). He also published an alternative hypothesis³ for the origin of the disease, and discussed his ideas in this interview. This claim, by Mullis and others, went on to have deadly consequences for AIDS patients in South Africa.
Now, given the use of PCR to identify the presence of HIV in AIDS patients, claiming that HIV was not implicated in AIDS must surely have involved a certain amount of mental gymnastics. However, as I’ve written elsewhere, the specific words sometimes attributed to him on this subject actually came from someone else.
Meanwhile, the use of PCR in detecting the presence of pathogens – and in all those other applications – continues apace.
¹ and its sequel. Yes, I know, this totally dates me.
² It’s Mullis we remember for this, but in fact the patent lists multiple researchers in addition to Mullis: H.A. Erlich, N. Arnheim, G.T. Horn, R.K. Saiki, & S.J. Scharf. Erlich & Arnheim led the team that demonstrated conclusively that the technique worked.
³ In the absence of any actual data it is hardly surprising that this proposal didn’t take off.