Molecular diagnosis, clinical evaluation and phenotypic spectrum of Townes-Brocks syndrome: insights from a large Chinese hearing loss cohort

BACKGROUND

Townes-Brocks syndrome (TBS) is a rare genetic disorder characterised by multiple malformations. Due to its phenotypic heterogeneity and rarity, diagnosis and recognition of TBS can be challenging and there has been a lack of investigation of patients with atypical TBS in large cohorts and delineation of their phenotypic characteristics.

METHODS

We screened SALL1 and DACT1 variants using next-generation sequencing in the China Deafness Genetics Consortium (CDGC) cohort enrolling 20 666 unrelated hearing loss (HL) cases. Comprehensive clinical evaluations were conducted on seven members from a three-generation TBS family. Combining data from previously reported cases, we also provided a landscape of phenotypes and genotypes of patients with TBS.

RESULTS

We identified five novel and two reported pathogenic/likely pathogenic (P/LP) SALL1 variants from seven families. Audiological features in patients differed in severity and binaural asymmetry. Moreover, previously undocumented malformations in the middle and inner ear were detected in one patient. By comprehensive clinical evaluations, we further provide evidence for the causal relationship between SALL1 variation and certain endocrine abnormalities. Penetrance analysis within familial contexts revealed incomplete penetrance among first-generation patients with TBS and a higher disease burden among their affected offspring.

CONCLUSION

This study presents the first insight of genetic screening for patients with TBS in a large HL cohort. We broadened the phenotypic-genotypic spectrum of TBS and our results supported an underestimated prevalence of TBS. Due to the rarity and phenotypic heterogeneity of rare diseases, broader spectrum molecular tests, especially whole genome sequencing, can improve the situation of underdiagnosis and provide effective recommendations for clinical management.

Recurrent, founder and hypomorphic variants contribute to the genetic landscape of Joubert syndrome

BACKGROUND

Joubert syndrome (JS) is a neurodevelopmental ciliopathy characterised by a distinctive mid-hindbrain malformation, the 'molar tooth sign'. Over 40 JS-associated genes are known, accounting for two-thirds of cases.

METHODS

While most variants are novel or extremely rare, we report on 11 recurring variants in seven genes, including three known 'founder variants' in the Ashkenazi Jewish, Hutterite and Finnish populations. We evaluated variant frequencies in ~550 European patients with JS and compared them with controls (>15 000 Italian plus gnomAD), and with an independent cohort of ~600 JS probands from the USA.

RESULTS

All variants were markedly enriched in the European JS cohort compared with controls. When comparing allele frequencies in the two JS cohorts, the Ashkenazim founder variant (TMEM216 c.218G>T) was significantly enriched in American compared with European patients with JS, while MKS1 c.1476T>G was about 10 times more frequent among European JS. Frequencies of other variants were comparable in the two cohorts. Genotyping of several markers identified four novel European founder haplotypes.Two recurrent variants (MKS1 c.1476T>G and KIAA0586 c.428delG), have been detected in homozygosity in unaffected individuals, suggesting they could act as hypomorphic variants. However, while fibroblasts from a MKS1 c.1476T>G healthy homozygote showed impaired ability to form primary cilia and mildly reduced ciliary length, ciliary parameters were normal in cells from a KIAA0586 c.428delG healthy homozygote.

CONCLUSION

This study contributes to understand the complex genetic landscape of JS, explain its variable prevalence in distinct geographical areas and characterise two recurrent hypomorphic variants.

UK consensus recommendations for clinical management of cancer risk for women with germline pathogenic variants in cancer predisposition genes: RAD51C, RAD51D, BRIP1 and PALB2

Germline pathogenic variants (GPVs) in the cancer predisposition genes BRCA1, BRCA2, MLH1, MSH2, MSH6, BRIP1, PALB2, RAD51D and RAD51C are identified in approximately 15% of patients with ovarian cancer (OC). While there are clear guidelines around clinical management of cancer risk in patients with GPV in BRCA1, BRCA2, MLH1, MSH2 and MSH6, there are few guidelines on how to manage the more moderate OC risk in patients with GPV in BRIP1, PALB2, RAD51D and RAD51C, with clinical questions about appropriateness and timing of risk-reducing gynaecological surgery. Furthermore, while recognition of RAD51C and RAD51D as OC predisposition genes has been established for several years, an association with breast cancer (BC) has only more recently been described and clinical management of this risk has been unclear. With expansion of genetic testing of these genes to all patients with non-mucinous OC, new data on BC risk and improved estimates of OC risk, the UK Cancer Genetics Group and CanGene-CanVar project convened a 2-day meeting to reach a national consensus on clinical management of BRIP1, PALB2, RAD51D and RAD51C carriers in clinical practice. In this paper, we present a summary of the processes used to reach and agree on a consensus, as well as the key recommendations from the meeting.

Awareness and Attitude Towards the Premarital Screening Programme Among High School Students in Muscat, Oman

Objectives

This study aimed to explore high school students' awareness and attitude towards premarital screening (PMS).

Methods

This cross-sectional study was conducted in 10 public high schools in Muscat, Oman from May to July 2016. A three-part self-administered questionnaire was used to collect data from grade 12 students. The first part focused on respondents' sociodemographic characteristics, while the second part dealt with awareness of the national PMS programme and the third part explored attitudes towards the national PMS programme.

Results

A total of 1,541 participants (response rate: 91.1%) completed the questionnaire. Most participants (78.1%) were aware of the availability of the PMS programme and their main source of information was family and friends (34.3%). The majority of students (87.4%) believed that PMS is important and most students (87.2%) indicated that they would undergo PMS. Over half of the students (55.3%) agreed that PMS should be mandatory before marriage and approximately one-third (38.3%) were in favour of having laws and regulations to prevent consanguineous marriages. Females were significantly more in favour of making PMS mandatory (P = 0.002) and enforcing PMS laws (P = 0.010) compared to males.

Conclusion

Most respondents had good levels of knowledge about the PMS programme and half thought it is important to be tested. However, some students were not in favour of PMS. Increasing awareness about Oman's PMS programme is important and motivating students could contribute significantly to increasing the utilisation of the PMS programme and to limiting genetic blood disorders.

Individual Radiosensitivity Assessment of the Families of Ataxia-Telangiectasia Patients by G2-Checkpoint Abrogation

Objectives

Ataxia-telangiectasia (A-T) is an autosomal recessive multisystem disorder characterised by cerebellar degeneration, telangiectasia, radiation sensitivity, immunodeficiency, oxidative stress and cancer susceptibility. Epidemiological research has shown that carriers of the heterozygous ataxia-telangiectasia mutated (ATM) gene mutation are radiosensitive to ionising irradiation and have a higher risk of cancers, type 2 diabetes and atherosclerosis. However, there is currently no fast and reliable laboratory-based method to detect heterozygous ATM carriers for family screening and planning purposes. This study therefore aimed to evaluate the ability of a modified G2-assay to identify heterozygous ATM carriers in the families of A-T patients.

Methods

This study took place at the Tehran University of Medical Sciences, Tehran, Iran, between February and December 2017 and included 16 A-T patients, their parents (obligate heterozygotes) and 30 healthy controls. All of the subjects underwent individual radiosensitivity (IRS) assessment using a modified caffeine-treated G2-assay with G2-checkpoint abrogation.

Results

The mean IRS of the obligate ATM heterozygotes was significantly higher than the healthy controls (55.13% ± 5.84% versus 39.03% ± 6.95%; P <0.001), but significantly lower than the A-T patients (55.13% ± 5.84% versus 87.39% ± 8.29%; P = 0.001). A receiver operating characteristic (ROC) curve analysis of the G2-assay values indicated high sensitivity and specificity, with an area under the ROC curve of 0.97 (95% confidence interval: 0.95-1.00).

Conclusion

The modified G2-assay demonstrated adequate precision and relatively high sensitivity and specificity in detecting heterozygous ATM carriers.

Should Premarital Screening for Blood Disorders be an Obligatory Measure in Oman?

Due to the high rate of consanguineous marriages in Oman, there is a correspondingly high prevalence of hereditary blood disorders, particularly sickle cell disease and β-thalassaemia. This article proposes the possibility of implementing mandatory premarital carrier screening for blood disorders in Oman, while giving due consideration to potential social and cultural obstacles. Although the implementation of such legislation would require collaboration between different sectors and may negatively affect the autonomy of certain individuals, mandatory premarital screening would help to alleviate the burden of hereditary blood disorders on the national healthcare system, as well as reduce avoidable suffering among carriers and their families.