TTI2 and Cognitive impairment: Subsequently, Langouet et al. found that a missense c.1307T > A (p.Ile436N) mutation in TTI2 causes a human autosomal recessive condition characterized by severe cognitive impairment, microcephaly, behavioral troubles, short stature, skeletal anomalies, and facial dysmorphic features (Langouët et al., 2013).