ABSTRACT
PURPOSE: Treacher Collins syndrome (TCS) is a rare autosomal dominant mandibulofacial dysostosis, with a prevalence of 0.2-1/10,000. Features include bilateral and symmetrical malar and mandibular hypoplasia and facial abnormalities due to abnormal neural crest cell (NCC) migration and differentiation. To date, three genes have been identified: TCOF1, POLR1C, and POLR1D. Despite a large number of patients with a molecular diagnosis, some remain without a known genetic anomaly. METHODS: We performed exome sequencing for four individuals with TCS but who were negative for pathogenic variants in the known causative genes. The effect of the pathogenic variants was investigated in zebrafish. RESULTS: We identified three novel pathogenic variants in POLR1B. Knockdown of polr1b in zebrafish induced an abnormal craniofacial phenotype mimicking TCS that was associated with altered ribosomal gene expression, massive p53-associated cellular apoptosis in the neuroepithelium, and reduced number of NCC derivatives. CONCLUSION: Pathogenic variants in the RNA polymerase I subunit POLR1B might induce massive p53-dependent apoptosis in a restricted neuroepithelium area, altering NCC migration and causing cranioskeletal malformations. We identify POLR1B as a new causative gene responsible for a novel TCS syndrome (TCS4) and establish a novel experimental model in zebrafish to study POLR1B-related TCS.
Subject(s)
Craniofacial Abnormalities/genetics , DNA-Directed RNA Polymerases/genetics , Mandibulofacial Dysostosis/genetics , Nuclear Proteins/genetics , Phosphoproteins/genetics , Animals , Apoptosis/genetics , Cell Differentiation/genetics , Cell Movement/genetics , Craniofacial Abnormalities/pathology , Genetic Predisposition to Disease , Humans , Mandibulofacial Dysostosis/pathology , Mutation , Neural Crest/abnormalities , Neural Crest/pathology , Tumor Suppressor Protein p53/genetics , Exome Sequencing , Zebrafish/geneticsABSTRACT
OBJECTIVES: Neonatal hearing impairment is a common disorder with a prevalence of 1 to 2 worldwide, with significant consequences on overall development when rehabilitated too late. New-born hearing screening has been implemented in the 1990s in most European countries and the USA. The Upper-Normandy region of France has been conducting a pilot program since 1999. The aim of this prospective study was to evaluate and critically analyse it. METHODS: The Upper-Normandy universal new-born hearing screening program is performed in two steps. Between 1999 and 2004, first, we administered a Transient Evoked Oto Acoustic Emission (TEOAE) test was administered a few days after birth for healthy newborns without risk factors. For newborns admitted to a neonatal intensive care unit (NICU) or presenting risk factors, was administered an automated auditory brainstem response (AABR) test prior to discharge. Second, newborns who failed the initial hearing screening were retested as outpatients using TEOAE. Since 2004, infants who failed the initial screen were tested with AABR 3 to 4 weeks later as outpatients, providing an opportunity to compare the two protocols. RESULTS: Overall screening coverage in the Upper-Normandy region is 99.8%. First step coverage is 99.58% in well-infant nurseries and 97.09% in the NICU. The test-retest procedure during the first step and the use of AABR for the second resulted in higher follow-up rates and lower false positive rates. CONCLUSIONS: The Upper-Normandy region universal newborn hearing screening program facilitated diagnosis and rehabilitation of infants before age of 9 months, most notably when severe to profound hearing impairment was found.
