The MKS1-related genotype–phenotype correlation was proposed as follows: two null alleles of MKS1 result in MKS; one null allele and one non-truncating allele that leaves the B9-C2 domain intact result in JBTS; two non-truncating alleles result in Bardet–Biedl syndrome (BBS, MIM 615990) (Bader et al., 2016; Luo et al., 2020). This evidence concerns the gene MKS1 and Bardet-Biedl syndrome.