Mutations in TCF4, encoding a class I basic helix-loop-helix transcription factor, are responsible for Pitt-Hopkins syndrome, a severe epileptic encephalopathy associated with autonomic dysfunction

Abstract

Pitt-Hopkins syndrome (PHS) is a rare syndromic encephalopathy characterized by daily bouts of hyperventilation and a facial gestalt. We report a 1.8-Mb de novo microdeletion on chromosome 18q21.1, identified by array-comparative genomic hybridization in one patient with PHS. We subsequently identified two de novo heterozygous missense mutations of a conserved amino acid in the basic region of the TCF4 gene in three additional subjects with PHS. These findings demonstrate that TCF4 anomalies are responsible for PHS and provide the first evidence of a human disorder related to class I basic helix-loop-helix transcription-factor defects (also known as "E proteins"). Moreover, our data may shed new light on the normal processes underlying autonomic nervous system development and maintenance of an appropriate ventilatory neuronal circuitry.

Figure 1.

Frontal and profile views of patients 1–4 with PHS, with ages given in years (y). The consistent facial features associate enophthalmia, strabismus, and thin eyebrows in their midline portion; a large nose with high bridge and flared nostril; a protruding philtrum; M-shaped Cupid’s bow; fleshy lips, wide mouth with shallow and broad palate, and widely spaced teeth. The helices of the ears are dysplastic and thick. The traits coarsen with age, and the lower face gets more protruding.

Figure 2.

Brain MRI findings for patients with PHS. A, T1-weighted sagittal images. B and C, Coronal flair or T2 sequences. Anomalies consistently noticed include a thin corpus callosum and moderate hypoplasia of the frontal lobes (A), marked white-matter hyperintensity in the temporal poles (B), and small hippocampi (C). The brain stem is normal (A). Patient 1, Mild ventricular dilatation and moderate hyperintensity of the dentate nuclei at age 4.5 years. Patient 2, No ventricular dilatation but moderate hyperintensity of the dentale nuclei, observed at age 6.5 years. Patient 3, Mild ventricular dilatation and no abnormalities of the posterior fossa at age 6.5 years.

Figure 3.

Genetic analyses of patients with PHS. A, Chromosome 18 array-CGH ratio profile obtained for patient 1 that identifies deletion of a single clone at chromosome 18q21.1. The X-axis represents the distance, in base pairs, along the chromosome from the p telomere. The Y-axis represents the hybridization ratio (reference DNA vs. test DNA) plotted on a log₂ scale. Gray lines indicate thresholds for clone deletion or duplication (array ratio mean±4 SD). The figure also shows the Ensembl display of this region. B, TCF4 gene mutations and phylogenetic analysis of TCF4 proteins. The two de novo missense mutations (R276Q and R276W) identified in patients 2–4 are shown. ClustalW (National Center for Biotechnology Information) alignment of class I bHLH proteins orthologs are shown. Shadowed amino acids correspond to conserved glutamic and arginine residues constituting the E box–recognition motif.