Spectrum of genetic variants in 306 patients with non-syndromic hearing loss from Croatia.

AIM: To determine the spectrum and frequency of disease-causing variants in patients with non-syndromic hearing loss (NSHL) and to investigate the diagnostic yield of the applied genetic methods. METHODS: The study enrolled 306 unrelated patients with childhood-onset, mild-to-profound NSHL referred to Children's Hospital Zagreb for genetic testing between March 2006 and October 2023. The GJB2 variants were analyzed with the multiplex ligation-dependent probe amplification method and Sanger sequencing of the coding region of the GJB2 gene. In 21 patients negative for GJB2 biallelic variants, clinical exome sequencing (CES) was performed. RESULTS: Among 234 disease-associated GJB2 alleles detected, 19 were clinically relevant, of which 18 were reported as pathogenic/likely pathogenic. The c.35delG variant accounted for 73.5% of the mutated alleles. More than half of the patients with biallelic GJB2 variants (64/110, 58.2%) were 35delG homozygotes. Seventeen non-GJB2 variants were found in 10 genes (TECTA, NOG, SLC26A4, PCDH15, TMPRSS3, USH2A, GATA3, MYO15A, SOX10, COL2A1) in 11 participants, and 5 variants (in TECTA, NOG, PCDH15, and SOX10) were novel (29.4%). CONCLUSION: We were able to elucidate the genetic cause of hearing loss in 121 patients, with an overall diagnostic rate of 39.5%. The c.35delG was the most common variant. CES allowed us to diagnose almost half of the patients with HL; to distinguish NSHL from the syndromic form of HL in cases where the phenotype was unclear or where symptoms were absent from an early age; and to discover novel variants.

The first case report of distal 16p12.1p11.2 trisomy and proximal 16p11.2 tetrasomy inherited from both parents.

Recurrent copy number variants in the chromosomal region 16p11.2 are among the most frequent genetic causes of neurodevelopmental disorders. The increasing prevalence of brain structural anomalies is also associated with 16p11.2 deletions and duplications. We report on a four-year-old boy with microcephaly, trigonocephaly, and dysmorphic features. The patient also exhibited motor delay and autism spectrum disorder. Microarray analysis showed a single-copy gain of a 1.187 kb segment in the 16p12.1p11.2 region and a two-copy gain of a 525 kb segment in the 16p11.2 region. Parental analysis revealed a 1.7 Mb duplication at the 16p12.1p11.2 (BP1-BP5 region) in the father and a 525 kb duplication in the 16p11.2 region (BP4-BP5) in the mother. The patient inherited the entire abnormality from each parent and, as a result, presented with partial trisomy of the 16p12.1p11.2 region and partial tetrasomy of the 16p11.2 region. The MLPA P343 Autism-1 Probemix was used to verify the copy number gains in the 16p11.2 region detected by chromosomal microarray analysis. Double duplications are very rare chromosomal rearrangements. The phenotype for distal 16p12.1p11.2 trisomy (BP1-BP3) and proximal 16p11.2 (BP4-BP5) tetrasomy is unknown. To our knowledge, this is the first patient described in the literature who inherited 16p11.2 duplications from both parents.

Novel duplication on chromosome 16 (q12.1-q21) associated with behavioral disorder, mild cognitive impairment, speech delay, and dysmorphic features: case report.

We report on the 10-year follow-up and clinical, cytogenetic, and molecular investigation of a girl admitted for evaluation because of speech delay, learning difficulties, aggressive behavior, and dysmorphic facial features that included high forehead, round face, epicanthic folds, low-set dysplastic ears, flat nasal bridge, long flat philtrum, thin upper lip, small mouth, and short neck. The analysis of high-resolution GTG- and CTG-banding chromosomes suggested a de novo direct duplication of 16q12-q21 region and fluorescence in situ hybridization analysis with whole-chromosome specific 16 probe confirmed that the duplicated genetic material originated from the chromosome 16. Subsequently, array-based comparative genomic hybridization analysis with a≈75 kb resolution showed a 9.92 Mb gain on the long arm of chromosome 16 at bands q12.1 through q21. To the best of our knowledge, this is the first case of duplication 16q12.1q21 described in literature. Several genes within the duplicated region are possibly correlated with clinical features present in our patient. Clinical and cytogenetic findings were compared with the small number of reported patients with pure duplications 16q, partially overlapping the one in our patient. Clinical phenotype seems to be distinctive between the proximal-intermediate and intermediate-distal regions of the long arm of the chromosome 16. In particular, we observed a set of dysmorphic features that could present a characteristic dup 16q11.2-q13 phenotype. The present study illustrates the advantages of an integrative approach using both conventional and molecular techniques for the precise characterization and genotype-phenotype correlation in patients with dysmorphism, behavioral problems, and learning difficulties.

Screening of patients at risk for 22q11 deletion.

UNLABELLED: The aim of this study was to determine whether deletion 22q11.2 studies should become apart of a standardized diagnostic workup for selected groups of at risk patients. We prospectively investigated four cohorts of unselected patients referred because of 1) congenital heart defect (CHD), 2) palatal anomalies, 3) hypocalcaemia, 4) dysmorphic features suggestive of del 22q11.2. Fluorescence in situ hybridization analysis revealed deletion 22q11.2 in 9.4% (6/64) patients with CHD. From 18 patients referred because of the hypocalcaemia, six (33.3%) had 22q11.2 deletion. In the group of 31 children with dysmorphic traits, the diagnosis was confirmed in two (6.4%) patients. None of the 58 children with palatal anomalies showed evidence of 22q11.2 deletion. CONCLUSIONS: Testing for the 22q11.2 microdeletion can be recommended in all patients with conotruncal heart defects and in patients with hypocalcaemia. It should be also considered in patients presenting only with dysmorphic traits suggestive of del 22q11.2, while screening in patients with cleft palate is not warranted.