Identification and characterisation of spontaneous mutations causing deafness from a targeted knockout programme.

BACKGROUND: Mice carrying targeted mutations are important for investigating gene function and the role of genes in disease, but off-target mutagenic effects associated with the processes of generating targeted alleles, for instance using Crispr, and culturing embryonic stem cells, offer opportunities for spontaneous mutations to arise. Identifying spontaneous mutations relies on the detection of phenotypes segregating independently of targeted alleles, and having a broad estimate of the level of mutations generated by intensive breeding programmes is difficult given that many phenotypes are easy to miss if not specifically looked for. Here we present data from a large, targeted knockout programme in which mice were analysed through a phenotyping pipeline. Such spontaneous mutations segregating within mutant lines may confound phenotypic analyses, highlighting the importance of record-keeping and maintaining correct pedigrees. RESULTS: Twenty-five lines out of 1311 displayed different deafness phenotypes that did not segregate with the targeted allele. We observed a variety of phenotypes by Auditory Brainstem Response (ABR) and behavioural assessment and isolated eight lines showing early-onset severe progressive hearing loss, later-onset progressive hearing loss, low frequency hearing loss, or complete deafness, with vestibular dysfunction. The causative mutations identified include deletions, insertions, and point mutations, some of which involve new genes not previously associated with deafness while others are new alleles of genes known to underlie hearing loss. Two of the latter show a phenotype much reduced in severity compared to other mutant alleles of the same gene. We investigated the ES cells from which these lines were derived and determined that only one of the 8 mutations could have arisen in the ES cell, and in that case, only after targeting. Instead, most of the non-segregating mutations appear to have occurred during breeding of mutant mice. In one case, the mutation arose within the wildtype colony used for expanding mutant lines. CONCLUSIONS: Our data show that spontaneous mutations with observable effects on phenotype are a common side effect of intensive breeding programmes, including those underlying targeted mutation programmes. Such spontaneous mutations segregating within mutant lines may confound phenotypic analyses, highlighting the importance of record-keeping and maintaining correct pedigrees.

Vestibular dysfunction is a manifestation of 22q11.2 deletion syndrome.

The 22q11.2 deletion syndrome (22q11.2DS) is the second most common cause of developmental delay after Down syndrome. Impaired cognitive development is highly prevalent, but also motor abnormalities such as hypotonia and delays in achieving motor milestones are described. Instability is frequently detected in children, adolescents, and adults and is mostly attributed to their limited motor performance. Until now, vestibular function has not been investigated in these patients, despite the growing evidence that they often have inner ear malformations. The aim of this prospective study was to identify the presence and character of vestibular dysfunction in 22q11.2DS. We investigated 23 subjects with proven 22q11.2DS, older than the age of 12. We performed caloric testing and pendular rotation chair tests with videonystagmography, cervical vestibular-evoked myogenic potential (c-VEMP)-testing, and posturography. Additional otoscopy and audiometry were performed on all subjects. We found a unilateral caloric hypofunction in 55% of patients, a certain absent c-VEMP response in 15% of ears, an inconclusive c-VEMP response in 33% of ears, and abnormal posturography in 68% of patients, of whom 42% displayed a typical vestibular pattern. Remarkably, 90% revealed uni- or bilateral weak caloric responses, independent of caloric symmetry. Vestibular dysfunction is frequent in subjects with 22q11.2DS. This knowledge should be taken into account when assessing motor performance in these patients. Additional larger studies are needed to determine whether this dysfunction implicates a therapeutic potential.

Malformations of the middle and inner ear on CT imaging in 22q11 deletion syndrome.

The 22q11 deletion syndrome (22q11DS), the most frequent microdeletion syndrome in humans, presents with a large variety of abnormalities. A common abnormality is hearing impairment. The exact pathophysiological explanation of the observed hearing loss remains largely unknown. The aim of this study was to analyze the middle and inner ear malformations as seen on computer tomographic imaging in patients with 22q11DS. We retrospectively reviewed the charts of 11 22q11DS patients who had undergone a CT of the temporal bone in the past. Of the 22 examined ears, two showed an abnormal malleus and incus, 10 presented with a dense stapes superstructure, and three ears had an abnormal orientation of the stapes. With regard to the inner ear, 12 ears showed an incomplete partition type II with a normal vestibular aqueduct. In four ears the vestibule and lateral semicircular canal were composed of a single cavity, in 14 ears the vestibule was too wide, and three ears had a broadened lateral semicircular canal. These findings suggest that malformations of the stapes, cochlea, vestibule, and lateral semicircular canal are frequent in 22q11DS. To our knowledge, the current study involves the largest case series describing middle and inner ear malformations in 22q11DS. © 2016 Wiley Periodicals, Inc.

Prevalence of Otological Disease in Turner Syndrome: A Systematic Review.

INTRODUCTION: Girls and women with Turner syndrome (TS) present with multiple ear and hearing problems, ranging from external morphologic abnormalities to sensorineural or conductive hearing loss. The exact pathophysiology behind these otological diseases is not yet completely understood. The aim of this study is to provide a systematic review on the prevalence of otological disease in TS. METHODS: We conducted a systematic review according to the PRISMA guidelines. A database search was performed in PubMed, Embase, Web of Science, and Cochrane library. RESULTS: The prevalence of otological disease as external ear deformities (20-62%), recurrent otitis media (24-48%), and hearing loss (36-84%) is high in TS. The auditory phenotype in TS is complex and seems to be dynamic with CHL due to middle ear disease at young age and sensorineural hearing loss later in life. CONCLUSION: This systematic review of the literature confirms that otological disease is definitely part of the widely variable phenotype in Turner patients. Strong evidence is lacking on the exact prevalence numbers, emphasizing the need for more prospective data gathering. Growing insights in its pathophysiology will help in the understanding and management of hearing problems in TS across lifespan.

Congenital sternoclavicular dermoid sinus.

We report a case series of 8 patients, presenting with a congenital sinus in the region of the sternoclavicular joint. This rare malformation has only been reported in the Japanese dermatological literature under the name of "congenital dermoid fistula of the anterior chest region". It has to be distinguished from other congenital anomalies and requires complete excision.