Further delineation of Pitt-Hopkins syndrome: phenotypic and genotypic description of 16 novel patients.

Haploinsufficiency of the gene encoding for transcription factor 4 (TCF4) was recently identified as the underlying cause of Pitt-Hopkins syndrome (PTHS), an underdiagnosed mental-retardation syndrome characterised by a distinct facial gestalt, breathing anomalies and severe mental retardation. TCF4 mutational analysis was performed in 117 patients with PTHS-like features. In total, 16 novel mutations were identified. All of these proven patients were severely mentally retarded and showed a distinct facial gestalt. In addition, 56% had breathing anomalies, 56% had microcephaly, 38% had seizures and 44% had MRI anomalies. This study provides further evidence of the mutational and clinical spectrum of PTHS and confirms its important role in the differential diagnosis of severe mental retardation.