As ARNT is a 1q21 gene, we then examined whether its expression would be affected by 1q21 gain, a common CA featuring a high‐risk MM subtype.8 Strikingly, MM cell lines carrying 1q21 gain (eg, H929 and OPM‐2) displayed a robust increase in protein level of HIF‐1β, compared to those without this CA (eg, RPMI8226, Figure 1C; U266, data not shown). Here, ARNT is linked to Miyoshi myopathy.