Four things you should know about the HIV "cure" before you get too excited

The baby might not even have been infected in the first place.

The story everyone is talking about today is the HIV "cure" - the Mississippi baby who, after being blasted with a cocktail of anti-viral drugs at birth, is now, at two years old, apparently virus-free. But when reading the euphoric news stories about it here, here and here, you should bear the following in mind:

1. The baby may not even have been infected in the first place

Here's a weird section in the NYT version of the story. Have a read of the following two paragraphs - are the doctors certain or uncertain that the baby was infected?

“The one uncertainty is really definitive evidence that the child was indeed infected,” said Dr. Daniel R. Kuritzkes, chief of infectious diseases at Brigham and Women’s Hospital in Boston.

Dr. Persaud and some other outside scientists said they were certain the baby — whose name and gender were not disclosed — had been infected. There were five positive tests in the baby’s first month of life — four for viral RNA and one for DNA. And once the treatment started, the virus levels in the baby’s blood declined in the pattern characteristic of infected patients.

The tests are pretty good, but are not usually trusted as a basis for confirmed diagnosis at that early stage. It is normal practice to confirm positive tests at 6 weeks. But as this baby had already been treated by then, lowering its viral load (negative tests came back at 29 days), it would have been difficult to do this. There is a very small chance the baby was not infected.

The virus may not have yet taken a hold on the baby's cells in a permanent way. Here's the WSJ:

Cells in the baby "may have been infected—there was virus around," said Steven Deeks, an AIDS researcher at University of California at San Francisco. "But the cells being infected weren't the type that become long-lived reservoirs."

There is also a small chance the baby was immune to HIV anyway. Around 1 per cent of Caucasians in the US are naturally immune.

Now, these are small chances, but then this baby is an outlier. It was not part of a large study where such anomalies are ruled out. The scientists have said it is unlikely to be replicable. Any way you put it, the baby itself is an anomaly.

2. This "cure" has already been found, and has been used on newly-infected people since 1987. Even if the baby was infected, today's news would simply extend it to newborns.

Today's news applies only to babies. Newborns at that. And it's not really a new method - rather, it's the same idea as PEP: if you have only just been infected, you might avoid HIV if you are immediately given a large amount of anti-HIV drugs. What the scientists confirmed today is that, in terms of emergency treatment, newborns are the same as newly-infected people. 

Here's the NYT again:

“That goes along with the concept that, if you treat before the virus has had an opportunity to establish a large reservoir and before it can destroy the immune system, there’s a chance you can withdraw therapy and have no virus,” said Dr. Anthony S. Fauci, the director of the National Institute for Allergy and Infectious Diseases.

(Oh, and if you were wondering, someone has actually been cured of AIDs before. This was a man called Timothy Brown, a leukemia sufferer who received a bone-marrow transplant from a donor genetically resistant to HIV.)

3. This would not be breaking much ground in preventing HIV in newborns anyway, because we have a solution for that

In countries with access to top-notch medical care (ie western countries), the transference of HIV from mother to child is extremely rare. This is because mothers are treated with antiretroviral therapy during pregnancy - a very effective way of preventing HIV in newborns.

4. Newborns in countries without a solution for that probably wouldn't get this treatment anyway

In countries without access to top-notch medical care, there is no reason that this treatment would be available where antiretroviral pregnancy treatment isn't.

So what does the news mean? Well it means that a few babies in countries with access to this sort of care but whose mothers have somehow slipped through the net of normal practice can be saved. Joyous news. But not quite as joyous as everyone seems to be making out.

UPDATE: This blog originally said that HIV tests at birth couldn't be accurate, but this applies only to antibody tests. The tests on DNA/RNA, which were done in this case, have a greater (although not 100 per cent) degree of accuracy.

HIV cure: not necessarily.. Photograph: Getty Images

Martha Gill writes the weekly Irrational Animals column. You can follow her on Twitter here: @Martha_Gill.

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Personal experiences – not just biology – shape who you find attractive

Researchers find past experiences play a role in identifying why people are attracted to certain individuals.

A new study suggests personal experiences influence our attraction to our preferred partners. It was previously thought genes played a bigger role, as they do in forming other examples of behaviour and character traits. Just reflect on the number of times you've been singled out by a family member for acting like one of your parents, either offensively or in a praiseworthy way.

There are certain characteristics that lead people to judge particular faces as more attractive than others, such as the level of symmetry. However, people still dispute others' opinions when judging facial attractiveness – it's subjective. After all, what else is the purpose of the romantic lead's sassy best friend in any rom-com or book? Or just think how boring conversations with your friends would be without such intense and passionate disagreements.

The researchers used twins as participants in the study in order to monitor these differences and disagreements in opinion. This was necessary because twins are, by definition, genetically identical, allowing the scientists to rule out genetic differences as a reason in explaining their findings.

A total of 547 sets of identical twins and 214 sets of fraternal twins (siblings sharing half of their DNA) were asked to judge the facial attractiveness of 102 female faces and 98 male faces, and give each face a rating based on preference. The results showed, on average, the twins agreed with each other 48 per cent of the time, and disagreed on facial attractiveness 52 per cent. Had the numbers been closer for both the identical and fraternal groups, this would have shown genes were more influential in determining our levels of attraction to others.

The study concluded the reason behind this difference was primarily based on an individual's unique environmental factors (the scientific phrase for "past experiences"), at 78 per cent.

Previous studies have shown aesthetic preferences are based on a range of other factors too, including socioeconomic and cultural features, the rater's own facial features and also personality. (See, it's not always about looks.) The authors were also able to determine how our genes influence facial recognition during this same experiment, if not our preferences.

Discovering that a personality characteristic is influenced by our environment is another highlight in the field of behavioural genetics, as it was previously thought "nature beats nurture" in many aspects of an individual's behaviour. However, this study shows that a person's experiences are unique even between family members.