Mitchell-Riley syndrome iPSCs exhibit reduced pancreatic endoderm differentiation due to a mutation in RFX6

Mitchell-Riley syndrome (MRS) is caused by recessive mutations in the regulatory factor X6 gene ( ) and is characterised by pancreatic hypoplasia and neonatal diabetes. To determine why individuals with MRS specifically lack pancreatic endocrine cells, we micro-CT imaged a 12-week-old foetus homozygous for the nonsense mutation c.1129C>T, which revealed loss of the pancreas body and tail. From this foetus, we derived iPSCs and show that differentiation of these cells proceeds normally until generation of pancreatic endoderm, which is significantly reduced. We additionally generated an reporter allele by gene targeting in wild-type H9 cells to precisely define RFX6 expression and in parallel performed hybridisation for in the dorsal pancreatic bud of a Carnegie stage 14 human embryo. Both and , we find that RFX6 specifically labels a subset of PDX1-expressing pancreatic endoderm. In summary, is essential for efficient differentiation of pancreatic endoderm, and its absence in individuals with MRS specifically impairs formation of endocrine cells of the pancreas head and tail.