Dear Colleagues,

Hearing loss is one of the most common birth defects. The estimated prevalence of clinically relevant unilateral or bilateral hearing loss is 1 to 3 per 1000 live births, which nearly doubles in adolescence due to the cumulative addition of patients with progressive, acquired or late-onset genetic causes. The introduction of newborn hearing screening and childhood hearing surveillance programs has led, over the past 30 years, to early diagnoses, improved assessments and, more importantly, to potentially improved developmental outcomes, as treatments and rehabilitation strategies (including hearing aids and cochlear implants) can be provided much earlier.

Over 50% of childhood permanent hearing loss is caused by genetic factors, classified as syndromic or nonsyndromic based on the presence or absence of co-inherited physical or laboratory findings.

About 30% of genetic deficits are syndromic, with more than 400 described syndromes associated with a hearing defect. There are some clinical features that can immediately indicate a syndromic cause of deafness: these are, for example, retinal, renal, thyroid, cardiac and pigmentation disorders, and craniofacial and structural anomalies of the outer, middle and inner ear. Other forms require expertise to be recognized, as they initially appear as isolated (not syndromic). It is important to be aware of the syndromes involving a child's hearing loss in order to facilitate early diagnosis and targeted treatment, both preventive and supportive. A correct approach to targeted genetic testing can, in some syndromic cases, reduce a long sequence of investigations and can shorten the time for medical treatment and appropriate support.

Nonsyndromic hereditary hearing loss accounts for about 70% of genetic cases in children; it is most often caused by pathogenetic variants in a single gene, but there is extreme genetic and also clinical intra- and interfamilial heterogeneity. Since 1994, the year in which the first genetic locus associated with nonsyndromic hearing loss was discovered, the dedicated research and clinical practices have grown, with more than 6,000 causal variants identified in more than 120 genes discovered to date.

The genetic diagnosis of syndromic and nonsyndromic hearing loss is an exquisitely multi- and interprofessional activity. Importantly, when interpreting data from genomic sequencing, the designation of pathogenicity for a particular variant does not automatically clarify the diagnosis and prognosis of a disease: for example, there are cases in which missense variants have been identified in genes that are associated with both Usher syndrome and nonsyndromic hearing loss.

This Special Issue is aimed at interdisciplinary clinical and research groups with an interest in the clinical description of syndromic and nonsyndromic hearing loss, evaluation strategies to identify the genetic cause and accurate genotype–phenotype correlation, the management of specific pathological clinical cases, and the counseling of family members of a child with syndromic or nonsyndromic hearing loss. Authors are welcome to cover other specific topics that have not been mentioned but fall within the theme of this Special Issue.

Dr. Eva Orzan
Prof. Dr. Saba Battelino
Prof. Dr. Alessandra Murgia
Guest Editors

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• genetic hearing loss
• phenotype-genotype correlation
• syndromic and non syndromic hearing loss
• genetic counseling
• hearing screening
• cochlear implant
• inner ear
• management