Novel comprehensive diagnostic strategy in Pitt-Hopkins syndrome: clinical score and further delineation of the TCF4 mutational spectrum.

Pitt-Hopkins syndrome (PTHS), characterized by severe intellectual disability and typical facial gestalt, is part of the clinical spectrum of Rett-like syndromes. TCF4, encoding a basic helix-loop-helix (bHLH) transcription factor, was identified as the disease-causing gene with de novo molecular defects. While PTHS appears to be a recognizable clinical entity, it seems to remain underdiagnosed, especially when facial gestalt is less typical. With the aim to facilitate the diagnosis of PTHS and to increase its rate and specificity, we have investigated 33 novel patients and defined a Clinical Diagnosis Score. Analysis of 112 individuals (79 previously reported and 33 novel patients) allowed us to delineate the TCF4 mutational spectrum, with 40% point mutations, 30% small deletions/insertions, and 30% deletions. Most of these were private mutations and generated premature stop codons. Missense mutations were localized in the bHLH domain, which is a mutational hotspot. No obvious difference was observed between patients harboring truncating, missense mutations, or deletions, further supporting TCF4 haploinsufficiency as the molecular mechanism underlying PTHS. In this study, we have summarized the current knowledge of TCF4 molecular pathology, reported all the mutations in the TCF4 database (http://www.LOVD.nl/TCF4), and present a novel and comprehensive diagnostic strategy for PTHS.

Whalen S ，Héron D ，Gaillon T ，Moldovan O ，Rossi M ，Devillard F ，Giuliano F ，Soares G ，Mathieu-Dramard M ，Afenjar A ，Charles P ，Mignot C ，Burglen L ，Van Maldergem L ，Piard J ，Aftimos S ，Mancini G ，Dias P ，Philip N ，Goldenberg A ，Le Merrer M ，Rio M ，Josifova D ，Van Hagen JM ，Lacombe D ，Edery P ，Dupuis-Girod S ，Putoux A ，Sanlaville D ，Fischer R ，Drévillon L ，Briand-Suleau A ，Metay C ，Goossens M ，Amiel J ，Jacquette A ，Giurgea I ... -  《-》

Pitt-Hopkins syndrome-associated mutations in TCF4 lead to variable impairment of the transcription factor function ranging from hypomorphic to dominant-negative effects.

Sepp M ，Pruunsild P ，Timmusk T 《-》

Functional analysis of TCF4 missense mutations that cause Pitt-Hopkins syndrome.

Pitt-Hopkins syndrome (PTHS) is a rare developmental disorder associated with severe mental retardation, facial abnormalities, and intermittent hyperventilation. Autosomal dominant PTHS is caused by mutations in the transcription factor 4 (TCF4) gene, whereas NRXN1 and CNTNAP2 mutations are associated with autosomal recessive PTHS. To determine the impact of missense mutations on TCF4 function, we tested a panel of PTHS-associated mutations using a range of quantitative techniques. Mutations in the basic helix-loop-helix (bHLH) domain of TCF4 alter the subnuclear localization of the mutant protein and can attenuate homo- and heterodimer formation in homogenous time-resolved fluorescence (HTRF) assays. By contrast, mutations proximal to the bHLH domain do not alter the location of TCF4 or impair heterodimer formation. In addition, we show that TCF4 can transactivate the NRXN1β and CNTNAP2 promoters in luciferase assays. Here we find variable, context-specific deficits in the ability of the different PTHS-associated TCF4 mutants to transactivate these promoters when coexpressed with different bHLH transcription factors. These data demonstrate that PTHS-associated missense mutations can have multiple effects on the function of the protein, and suggest that TCF4 may modulate the expression of NRXN1 and CNTNAP2 thereby defining a regulatory network in PTHS.

Forrest M ，Chapman RM ，Doyle AM ，Tinsley CL ，Waite A ，Blake DJ ... -  《-》

The Pitt-Hopkins syndrome: report of 16 new patients and clinical diagnostic criteria.

Pitt-Hopkins syndrome (PTHS) is characterized by severe intellectual disability, typical facial gestalt and additional features, such as breathing anomalies. Following the discovery of the causative haploinsufficiency of transcription factor 4 (TCF4), about 60 patients have been reported. We looked for TCF4 mutations in 63 patients with a suspected PTHS. Haploinsufficiency of TCF4 was identified in 14 patients, as a consequence of large 18q21.2 chromosome deletions involving TCF4 (2 patients), gene mutations (11 patients) and a t(14q;18q) balanced translocation disrupting TCF4 (one patient). By evaluating the clinical features of these patients, along with literature data, we noticed that, in addition to the typical facial gestalt, the PTHS phenotype results from the various combinations of the following characteristics: intellectual disability with severe speech impairment, normal growth parameters at birth, postnatal microcephaly, breathing anomalies, motor incoordination, ocular anomalies, constipation, seizures, typical behavior and subtle brain abnormalities. Although PTHS is currently considered to be involved in differential diagnosis with Angelman and Rett syndromes, we found that combining the facial characteristics with a detailed analysis of both the physical and the neurological phenotype, made molecular testing for PTHS the first choice. Based on striking clinical criteria, a diagnosis of PTHS was made clinically in two patients who had normal TCF4. This report deals with the first series of PTHS patients of Italian origin.

Marangi G ，Ricciardi S ，Orteschi D ，Lattante S ，Murdolo M ，Dallapiccola B ，Biscione C ，Lecce R ，Chiurazzi P ，Romano C ，Greco D ，Pettinato R ，Sorge G ，Pantaleoni C ，Alfei E ，Toldo I ，Magnani C ，Bonanni P ，Martinez F ，Serra G ，Battaglia D ，Lettori D ，Vasco G ，Baroncini A ，Daolio C ，Zollino M ... -  《-》

263.4 kb deletion within the TCF4 gene consistent with Pitt-Hopkins syndrome, inherited from a mosaic parent with normal phenotype.

Pitt-Hopkins syndrome (PTHS) is a rare neurodevelopmental genetic disorder, remaining under-diagnosed due to similarities with other known genetic syndromes. It is mainly characterized by severe intellectual disability, overbreathing, a typical facial gestalt, tendency to epilepsy and is caused by TCF4 haploinsufficiency. We report on a 14-year old boy, born to healthy non-consanguineous parents, with a PTHS spectrum phenotype, presenting with moderate to severe developmental delay, severe speech delay and facial dysmorphism. Genetic investigation using array-based comparative genomic hybridization (array-CGH) with a 400K custom array, revealed a 263.4 kb deletion within the TCF4 gene, removing exons 4-9. Parental array-CGH analysis was also performed, indicating paternal mosaicism for the same deletion. The mosaicism was confirmed by Quantitative Real-Time PCR. The current report describes a new TCF4 deletion associated with a PTHS phenotype. Moreover, it is the first case to our knowledge, where such a deletion is shown to be inherited from a clinically unaffected mosaic parent. Our results highlight the importance of parental testing in this setting for more accurate and focused prenatal diagnosis. The level and tissue-specificity of mosaicism in the father would be an interesting direction for further studies.

Kousoulidou L ，Tanteles G ，Moutafi M ，Sismani C ，Patsalis PC ，Anastasiadou V ... -  《-》