Table 2. Bioinformatic analysis of the R206H and R258S substitutions.

	WT residue	Mutated residue	PolyPhen prediction	SIFTa prediction
ACVR1 p.R206H	Positively charged/ hydrophilic	Positively charged/ hydrophilic	Probably damagingb; PSIC score 2.348c	Affects protein function; score 0.00 (M 3.04; S 52)
ACVR1 p.R258S	Positively charged/ hydrophilic	Neutral/polar/hydrophilic/ Possible phosphorylation	Probably damagingb; PSIC score 2.764c	Affects protein function; score 0.00 (M 3.07; S 29)

PolyPhen and SIFT web services were queried to predict the effects on protein structure and function.

^aSIFT (sorting intolerant from tolerant) score is the normalized probability that the residue substitution is tolerated; score <0.05 indicates that the amino-acid change is predicted to affect the protein function.

^bPolyPhen results are empirically defined as follows: probably damaging – it is with high confidence likely to affect protein function or structure; possibly damaging – it is supposed to affect protein function or structure; benign – most likely lacking any phenotypic effect; unknown – the lack of data do not allow PolyPhen to make a prediction.

^cA PSIC score >2 indicates that the substitution is predicted to be damaging for protein structure or function and is only rarely or never observed in this position among different species

M represents the ‘median sequence information', a parameter measuring the diversity of the sequences used for prediction. S represents the number of sequences used for alignments at the position of the substitution. Sequences with gaps in the region are not considered.