Six individuals with probable loss-of-function RFX4variants have been identified. Three were individuals who harbored de novoRFX4variants, including an in-frame deletion (RFX4 p.(Tyr639_Ser643del)), and two predicted damaging missense variants (RFX4 p.(Arg79Ser) and p.(Thr362Ala)). Three additional related individuals (siblings) were homozygous for a missense variant in RFX4(p.Thr247Met) altering a well-conserved threonine residue. Parents of these siblings were first cousins, each heterozygous for the mutation and without any known neurobehavioral phenotype, and a heterozygous sibling was similarly reported as neurotypical; this pedigree therefore raises the possibility that the RFX4phenotype may be associated with both monoallelic and biallelic inheritance as has been described for several other genetic conditions.
RFX4exhibits intolerance to loss-of-function variation in human population databases (gnomAD, pLI scores = 1.00). All variants were absent from gnomAD. All missense variants affect highly conserved amino acids (PhastCons vertebrate, mammalian, and primate scores ranging from 0.99–1.00).
RFXtranscription factors are defined by a conserved, specialized winged-helix type DNA binding domain (DBD) that recognize the X-box motif. In addition to the DBD, RFX4has three known domains that are associated with dimerization (DD). RFX4variants did not exhibit clustering to specific functional domains.
RFX4has been reported to have relatively high expression in human cortex. Single-cell transcriptomes from developing and adult human cortex revealed that in developing human cortex, RFX4is most highly expressed in outer radial glia, and in adult cortex RFX4was most highly expressed in astrocytes. These expression profiles suggest that RFXdeleterious variants may lead to our observed neurodevelopmental phenotypes by altering early developmental cell fates or by impacting the function of astrocytes.
RFX4