Interesting study suggests one of the mutations that distinguishes two early lineages (A & B) of #SARSCoV2 in Wuhan has functional effect. Here's my summary of evolutionary relevance of this pre-print by @Digs66768072 @nisha_kriplani @dr_sara_c biorxiv.org/content/10.110… 👇🧵
Early #SARSCoV2 from sequences Dec-2019 and Jan-2020 are all closely related as expected in new outbreak. But there is some genetic variation. One classification system (proposed by @arambaut et al) divides early #SARSCoV2 sequences into lineages A and B (nature.com/articles/s4156…)
Lineage A is closer to bat coronaviruses, and so is probably more similar to first virus that entered humans. Lineage B has two mutations that make it more different from bat coronaviruses (T8782C & C28144T), and so probably descends from lineage A. As paper above says: 
The Huanan Seafood Market super-spreading event involved lineage B, which went on to dominate globally. Below are trees from academic.oup.com/mbe/advance-ar… showing relationship of lineage B (large circle at bottom) & lineage A (all other circles) for two plausible outgroup rootings:
Anyway, so far the mutations that distinguish lineage A and B have just been genetic markers useful for tracing virus's evolution and classifying sequences into different lineages. But the new pre-print (biorxiv.org/content/10.110…) mentioned at top of this thread changes that.
Specifically, this pre-print looks at the functional effect of the amino-acid change caused by nucleotide mutation C28144T, which recall is one of the two mutations that makes lineage B more different from bat coronaviruses than lineage A.
That mutation changes residue 84 in the ORF8 protein from Ser to Leu. Pre-print shows secreted ORF8 modulates ability of macrophages to secrete cytokines. And the two different variants at residue 84 lead to different changes in secretion of cytokines such as IL-6, IL-8, and MIF.
These results imply the C28144T nucleotide mutation (Ser84->Leu ORF8 amino-acid mutation) could subtly alter immune response to infection. Because relationship between cytokine expression and overall infection/disease is complex...
... it's not possible to say if or how the mutation might impact either viral transmission or disease severity. But the results do suggest that we should consider the possibility that this early lineage-defining mutation has a functional effect.
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