Despite this, there have been reports of IRD patients with AI,27, 28, 29 with one suggesting that AI is a common finding in IRD patients.27 A recent study described a family with a homozygous missense variant in PEX6 with a combination of microcephaly, developmental delay, white matter changes, AI as well as sensory defects.26 Therefore it is difficult to assign individuals to HS or IRD diagnoses as it is becoming increasingly clear that their phenotypes appear to overlap. This evidence concerns the gene PEX6 and Global developmental delay.