MPLKIP and trichothiodystrophy: The cellular roles of TTDN1 are unclear, but mutations in the TTDN1 gene cause a form of trichothiodystrophy (TTD) referred to as non‐photosensitive (NPS) TTD (Nakabayashi et al, 2005; Heller et al, 2015) typified by seizures and symptoms seen in CDKL5‐associated diseases (Heller et al, 2015).