TCF7L2 and Intellectual disability: This gene (TCF4, Gene ID: 6925) is often confused with the transcription factor 7-like 2 gene (Gene ID: 6934, official gene symbol: TCF7L2), which is downstream of the WNT pathway and referred to as T-cell factor 4 and often mistakenly abbreviated as TCF4. Haploinsufficiency of TCF4 is known to cause Pitt–Hopkins syndrome, which is characterized by developmental delays with severe intellectual disability, dysmorphic facial features, and episodic hyperventilation and/or breath-holding while awake, among other features.