Broadening the phenotype associated with mutations in UPF3B: two further cases with renal dysplasia and variable developmental delay.

We present two brothers with mutations in UPF3B, an X-linked intellectual disability gene. Our family consists of two affected brothers and a carrier mother. Both affected brothers had renal dysplasia. A maternal uncle died from a congenital heart defect at 4 months. The two boys had variable degrees of developmental delay. One had macrocephaly, significant expressive speech delay and constipation. The other brother had normocephaly, obsessional tendencies and was diagnosed with high functioning autism. The phenotypically normal mother had 100% skewed X-inactivation. Our cases expand the phenotype seen with UPF3B mutations and highlight the variability within families.