Interstitial duplication in the proximal long arm of chromosome 16

Clinical Features of de novo Pure 16q21q24.1 Chromosome Duplication

Pure partial duplications of the long arm of chromosome 16 are rare and few cases are described with delineation by chromosomal microarray. Data about clinical abnormalities of pure partial 16q duplications are incomplete because many individuals die during the perinatal period. We describe the clinical features of a 47-month-old Brazilian girl with 16q21q24.1 duplication. To the best of our knowledge, she is the first person with this specific chromosome segment duplication, and we compare her phenotype with the only reported individual alive with intermediate-distal pure 16q duplication.

A duplication on chromosome 16q12 affecting the IRXB gene cluster is associated with autosomal dominant cone dystrophy with early tritanopic color vision defect

Cone dystrophies are a rare subgroup of inherited retinal dystrophies and hallmarked by color vision defects, low or decreasing visual acuity and central vision loss, nystagmus and photophobia. Applying genome-wide linkage analysis and array comparative genome hybridization, we identified a locus for autosomal dominant cone dystrophy on chromosome 16q12 in four independent multigeneration families. The locus is defined by duplications of variable size with a smallest region of overlap of 608 kb affecting the IRXB gene cluster and encompasses the genes IRX5 and IRX6. IRX5 and IRX6 belong to the Iroquois (Iro) protein family of homeodomain-containing transcription factors involved in patterning and regionalization of embryonic tissue in vertebrates, including the eye and the retina. All patients presented with a unique progressive cone dystrophy phenotype hallmarked by early tritanopic color vision defects. We propose that the disease underlies a misregulation of the IRXB gene cluster on chromosome 16q12 and demonstrate that overexpression of Irx5a and Irx6a, the two orthologous genes in zebrafish, results in visual impairment in 5-day-old zebrafish larvae.

A Very Rare Partial Trisomy Syndrome: De Novo Duplication of 16q12.1q23.3 in a Turkish Girl with Developmental Delay and Facial Dysmorphic Features

Trisomy 16 is the most common type of autosomal trisomy associated with spontaneous abortion and is incompatible with life. Upon examining previously reported cases of partial chromosome 16q duplication, it was noted that the majority of cases had complex chromosomal abnormalities due to parental balanced chromosomal translocation carriage. The clinical presentation of very rare pure partial trisomy 16q cases was associated with congenital anomalies, facial dysmorphic findings and intellectual disability. In this study, we evaluated the physical characteristics and genetic data of an 8-month-old girl with developmental delay and facial dysmorphic features. Dysmorphic features including prominent metopic suture, synophrys, asymmetric head shape, triangular and asymmetric face, telecanthus, epicanthal folds, down-slanting palpebral fissures, microphthalmia of the left eye, anteverted nares, smooth and tented philtrum, microretrognathia, low-set posteriorly rotated ears, auricular pits, high-arched palate, thin upper lip and hypotonia were recorded. Her karyotype was 46,XX,add(16)(q24). To identify the extension of the duplicated section, array comparative genomic hybridization (aCGH) analysis was performed, which showed a de novo 29.8 Mb duplication [arr[hgl9] 16q12.1q23.3(52459169-82285105) x 3], interpreted to be pathogenic. We present this case report to clarify the clinical findings of a rare chromosomal anomaly, discuss the genes that may be related to the phenotype and advance the literature in terms of knowledge regarding genotypephenotype correlation.

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.