The reported patients with DNAJC12 deficiency usually receive BH4 with or without l‐dopa/carbidopa/5‐hydroxytryptophan treatment; as a result, BH4 supplementation not only supports in the aromatic amino acid hydroxylases (PAH, TH, and TPH) reactions, but also acts as a pharmacological chaperone that increases the stability of these enzymes similar to that occurs in BH4‐responsive PKU (Anikster et al., 2017; de Sain‐van der Velden, 2018). Here, TPH1 is linked to hyperinsulinemic hypoglycemia, familial, 4.