Scalet et al. (2018) provide experimental evidence of the endogenous U5 supporting modified U1 snRNA to achieve the correction of aberrant splicing of the FAH gene (encodes an enzyme of the tyrosine I catabolism; FAH deficiency, Hereditary Tyrosinemia type I, HTI is associated with cirrhosis and hepatocellular carcinoma). Here, FAH is linked to hyperinsulinemic hypoglycemia, familial, 4.