Genetic evaluation of American minority pediatric cochlear implant recipients

Evaluating parental genetic knowledge of hearing loss with and without pre-test genetic counseling in a pediatric otolaryngology clinic

This study evaluated parental knowledge of genetics of sensorineural hearing loss (SNHL) and satisfaction following pre-test consult with and without genetic counseling (GC). A survey evaluating parents' knowledge of genetics for SNHL with and without GC was administered to parents of children with SNHL who were offered genetic testing. The survey also inquired about satisfaction, and decision to pursue genetic testing. Statistical tests included Fisher-Freeman-Halton test and Mann-Whitney test. Forty-nine participants completed the survey and were seen by both otolaryngology and GC intern (ENT + GC) (n = 24) or by otolaryngology (ENT) only (n = 25). Participation groups were not randomized. There were no significant differences in demographics between groups. Participants in the ENT + GC group had higher average genetics knowledge score of 72% correct (range 22%-100%), compared to the ENT only group with 44% (range 22%-78%) (p < .001). Participants in the ENT + GC group were more likely to know the different test result possibilities (p = .002), the most common form and pathogenic variant associated with SNHL (p < .001), that only a subset of genes are evaluated (p = .004), and that genetic testing may not explain SNHL etiology (p = .013), in comparison with the ENT only group. There was no significant difference in parental satisfaction or ultimate decision to undergo testing between groups. Obtaining genetic testing plays an integral role in the diagnosis and management of SNHL in the pediatric population. Our results suggest that the addition of GC increases parent knowledge of genetics and SNHL. This knowledge allows the family to make a more informed decision as to whether or not to pursue genetic testing.

Systematic Review of Hearing Loss Genes in the African American Population

OBJECTIVE

Literature review of the genetic etiology of hearing loss (HL) in the African American (AA) population.

DATA SOURCES

PubMed, EBSCO, and CINAHL were accessed from 1966 to 2018.

REVIEW METHODS

PRISMA guidelines were followed. Search terms included permutations of "hearing loss," "African American," "black," and "genetic"; "African American" was then cross-referenced against documented HL genes. AA subjects included in multiethnic cohorts of genetic HL testing were identified by searching the key terms "hearing loss" and "ethnic cohort" and "genetic." The Q-Genie tool was used in the quality assessment of included studies. An allele frequency meta-analysis of pathogenic GJB2 variants in the AA population was performed and stratified by hearing status.

RESULTS

Four hundred seventeen articles were reviewed, and 26 met our inclusion criteria. Ten studies were included in the GJB2 meta-analysis. In the general AA population, pathogenic GJB2 variants are rare, including the 35delG allele, which displayed a carrier frequency of 0.05%. Pathogenic variants were discovered in seven nonsyndromic HL genes (GJB2, MYO3A, TECTA, STRC, OTOF, MYH14, TMC1), eight syndromic HL genes, and one mitochondrial HL gene. Recent comprehensive genetic testing using custom genetic HL testing platforms has yielded only a 26% molecular diagnosis rate for HL etiologies in the AA population.

CONCLUSIONS

Investigators should be encouraged to provide an ethnic breakdown of results. Sparse literature and poor diagnosis rates indicate that genes involved in HL in the AA population have yet to be identified. Future explorative investigations using next-generation sequencing technologies, such as whole-exome sequencing, into the AA population are warranted.

A Novel C-Terminal CIB2 (Calcium and Integrin Binding Protein 2) Mutation Associated with Non-Syndromic Hearing Loss in a Hispanic Family

Hearing loss is a complex disorder caused by both genetic and environmental factors. Previously, mutations in CIB2 have been identified as a common cause of genetic hearing loss in Pakistani and Turkish populations. Here we report a novel (c.556C>T; p.(Arg186Trp)) transition mutation in the CIB2 gene identified through whole exome sequencing (WES) in a Caribbean Hispanic family with non-syndromic hearing loss. CIB2 belongs to the family of calcium-and integrin-binding (CIB) proteins. The carboxy-termini of CIB proteins are associated with calcium binding and intracellular signaling. The p.(Arg186Trp) mutation is localized within predicted type II PDZ binding ligand at the carboxy terminus. Our ex vivo studies revealed that the mutation did not alter the interactions of CIB2 with Whirlin, nor its targeting to the tips of hair cell stereocilia. However, we found that the mutation disrupts inhibition of ATP-induced Ca2+ responses by CIB2 in a heterologous expression system. Our findings support p.(Arg186Trp) mutation as a cause for hearing loss in this Hispanic family. In addition, it further highlights the necessity of the calcium binding property of CIB2 for normal hearing.

Is deafness etiology important for prediction of functional outcomes in pediatric cochlear implantation?

CONCLUSIONS

Implanted children with GJB2 mutations tended to achieve better functional outcomes than the two control groups, although clear-cut significance was not always achieved. Hearing loss etiology may be considered as one of the important predictors, but complex influence of other factors on postoperative performance should be included in cautious individual counseling.

OBJECTIVE

This study aimed to detect possible associations between hearing loss etiology and postoperative rehabilitation outcomes in prelingually deaf children, with a particular focus on hereditary deafness caused by connexin mutations.

METHODS

Eighty-one of 92 prelingually deaf implanted children, tested for DFNB1 mutations, were divided into 3 etiology groups and underwent audiological evaluation in tone audiometry, speech audiometry, monosyllabic words, and categories of auditory performance (CAP), conducted 1, 3, and 5 years after implantation.

RESULTS

Statistically significant differences (p < 0.05) for tone audiometry were obtained, particularly after the first and third year post implantation, between 'connexin' and 'known' etiology groups. In speech audiometry, the monosyllabic word test, and CAP, the connexin group of children scored significantly better than the two control groups only after 3 and 5 years. Although the rate of excellent performers was higher in the connexin group, poor results were achieved in all groups in similar proportion.

Mutational analysis of the SLC26A4 gene in Chinese sporadic nonsyndromic hearing-impaired children

OBJECTIVE

To investigate the mutations of SLC26A4 gene and the relevant phenotype in Chinese sporadic nonsyndromic hearing-impaired children.

METHODS

195 Chinese sporadic nonsyndromic hearing-impaired children were subjected to microarray-based mutation detection for 9 hot spot mutations in four of the most common deafness-related genes (GJB2, SLC26A4, GJB3, and 12s rRNA). Subsequently, twenty-one patients with one SLC26A4 mutation detected by microarray were subjected to sequencing analysis of the whole SLC26A4 coding region and the splice sites in order to identify the second mutant allele. The inner ear malformation and hearing loss level were compared among different genotypes.

RESULTS

The incidence of genetic mutations was found to be 43.59% (85/195) in this patient group using CapitalBio Deafness Gene Mutation Detection Array Kit. A total of 34 children (17.44%) were found carrying the mutant SLC26A4 sequences. Thirteen (6.67%) children carried two mutant alleles of SLC26A4 and 21 (10.77%) children carried one mutant allele of SLC26A4. After the application of subsequent sequencing analysis, 13 mutational variants including 4 novel variants, two missense (p.D661G, p.N457D), one splice site mutation (IVS15+1G>A) and one frameshift mutation (624_632del9insACTTGGC), were identified in SLC26A4 gene in 15 of the 21 previously monoallelic patients. No second mutation was identified in the remaining 6 children. Biallelic mutations of SLC26A4 were identified in 20 of 21 children with enlarged vestibular aqueduct.

CONCLUSIONS

Our results demonstrated that genetic factors were important causes for sporadic nonsyndromic hearing loss in Chinese pediatric cases. Mutation of SLC26A4 is one of the major genetic causes in nonsyndromic hearing loss with inner ear malformation. IVS7-2A>G, 2168A>G and 1229C>T were the most frequent mutations identified in our studies. The combination of microarray testing and sequencing analysis is a useful and high-throughput method for the diagnosis of genetic hearing loss.

Minimally invasive genetic screen for GJB2 related deafness using dried blood spots

OBJECTIVE

Nonsyndromic hearing loss is one of the most abundant human sensory disorders, and can be found in 1 out of 1000 newborns. In 60-70% of the cases this disorder is hereditary. The phenotype varies from moderate hearing loss to almost complete deafness, often only revealed in late childhood. Early detection of hearing related genetic variations in the first few weeks of life would allow planning of the audiological and logopedical procedures to maintain the children's normal audiological and speech development, and if required a cochlear implantation can be planned in time. We wanted to evaluate, whether the blood samples collected from neonates onto Guthrie cards (dried blood spots, or DBS), and blood collected from people of various ages into blood collecting tubes is equally usable for genetic testing. The quality of the samples on DBS's for genetic tests after an extended period of storage was evaluated. The methods for sample preparation and analysis were also evaluated.

METHODS

Two DNA extraction methods were compared on the samples. We extracted DNA from whole blood with the Versagene Blood Kit from Gentra, and from DBS's with boiling. Allele-specific PCRs (AS-PCR) were carried out on each sample. Samples were analyzed with AS-PCR and sequencing, for the 35delG mutation in the GJB2 (Cx26) gene. Freshly drawn and dried blood spot samples stored for several years were used in the experiments.

RESULTS

An AS-PCR method for detecting 35delG mutation on DNA extracted from Guthrie cards was validated. Blood samples up to 10 years of storage were applicable in the screen. 84 patients were found with 35delG mutations, both heterozygous (with no detected hearing related phenotypical discrepancies), and homozygous (phenotipically with moderate to severe hearing loss) forms.

CONCLUSIONS

The dried blood spots on Guthrie cards require only three drops of blood to be collected from children, which causes less stress than taking 3 ml of blood. The blood stored on Guthrie cards can be used to store DNA samples for at least 10 years. Even under suboptimal storage conditions the samples' DNA remains intact for genetic testing. Compared to blood collection tubes Guthrie cards cost less, are easier to transport and store.