Recently, Aminoff et al. described a maternal UPD4 case with abetalipoproteinemia caused by a homozygous mutation of the MTTP gene [36]; Losekot et al. described a polycystic kidney disease in a maternal UPD4 case due to a homozygous mutation in the PKD2 gene [23]. This evidence concerns the gene MTTP and polycystic kidney disease.