Given that there are many 1000s of potential positive variants, the implication is clear: If a human being could be engineered to have the positive version of each causal variant, they might exhibit cognitive ability which is 100 standard deviations above average. This corresponds to more than 1000 IQ points.

or perhaps merely 550:

Most humans have 1000 rare (-) alleles for intelligence and height, and someone who is 1 standard deviation above average has 30 fewer (-) variants. A human with none of the negative alleles might be 30 SD above average! Such a person has yet to exist in human history. When current IQ tests were developed, the median raw score of the norming sample is defined as IQ 100 and scores each standard deviation (SD) up or down are defined as 15 IQ points greater or less, although this was not always so historically. By this definition, 95% of the population scores an IQ between 70 and 130, which is within 2 standard deviations of the mean. 30 SD above average would be an IQ of 550.

here is an urgent rationale to increase everyone’s IQ by 30 points: survival of the species depends on it. our problems are getting harder faster than our ability to adapt, and you need a level of intelligence to set aside your short term aims in favor of a global view. my guess would be that’s around 130. the linked article has proposals how to bring in the rear, which is a great start. and there’s also more modest proposals:

KL-VS did not curb decline, but it did boost cognitive faculties regardless of a person’s age by the equivalent of 6 IQ points. KL-VS will be the most important genetic agent of non-pathological variation in intelligence yet discovered.

another overview:

individual differences in human intelligence can 50%–80% be explained by genetic influences making intelligence one of the most heritable traits. However, present GWAS studies can capture 22% of this heritability. Each gene has a small effect on intelligence. 95% of the genetic variants are located in intronic and intergenic regions and might have a gene regulatory function. 1.4% of associated SNPs are located in DNA fragments that are translated into protein. By 2025, between 100M and 2B human genomes could be sequenced.

and it goes beyond IQ too:

There are people with rare but highly beneficial genes. Adult whole-body gene therapy could make what is currently good and rare into something that is common or universal.

2023-12-15: A sketch how IQ augmentation in adults might be possible

1. Determine if it is possible to perform a large number of edits in cell culture with reasonable editing efficiency and low rates of off-target edits.
2. Run trials in mice. Try out different delivery vectors. See if you can get any of them to work on an actual animal.
3. Run trials in cows. We have good polygenic scores for cow traits like milk production, so we can test whether or not polygenic modifications in adult animals can change trait expression.
4. (Possibly in parallel with cows) run trials on chimpanzees
   The goal of such trials would be to test our hypotheses about mosaicism, cancer, and the relative effect of genes in adulthood vs childhood.
5. Run trials in humans on a polygenic brain disease. See if we can make a treatment for depression, Alzheimer’s, or another serious brain condition.
6. If the above passes a basic safety test (i.e. no one in the treatment group is dying or getting seriously ill), begin trials for intelligence enhancement.