Narrowing the deleted region associated with the 15q21 syndrome

Clinical and molecular characterization of a patient with 15q21.2q22.2 deletion syndrome

We report on a 16-year-old girl with a complex phenotype, including intellectual disability, facial dysmorphisms, and obesity. During her infancy, she presented with weak sucking, global developmental delay, and later with excessive eating with central obesity. The girl was clinically diagnosed with probable Prader-Willi syndrome. Chromosomal analysis showed a de novo deletion 46,XX,del(15)(q21q22). However, the use of the Affymetrix CytoScan HD Array defined the exact breakpoints of the deleted 15q21q22 region. The imbalance, about 10.5 Mb in size, is to date the second largest deletion ever described in this chromosomal region. In addition, our patient carries a microdeletion in the 1q44 region and a gain in 9p24. The array result was arr[hg19] 9p24.1(6,619,823-6,749,335)×3, 1q44(248,688,586-248,795,277)×1, 15q21.2 q22.2(50,848,301-61,298,006)×1. Although our patient presents additional chromosomal alterations, we provide a correlation between the clinical findings and the phenotype of the 15q21 deletion syndrome.

De novointerstitial deletion of 15q22q23 with global developmental delay and hypotonia: the first Korean case

Interstitial deletions involving the chromosome band 15q22q24 are very rare and only nine cases have been previously reported. Here, we report on a 12-day-old patient with a de novo 15q22q23 interstitial deletion. He was born by elective cesarean section with a birth weight of 3,120 g at 41.3-week gestation. He presented with hypotonia, sensory and neural hearing loss, dysmorphism with frontal bossing, flat nasal bridge, microretrognathia with normal palate and uvula, thin upper lip in an inverted V-shape, a midline sacral dimple, severe calcanovalgus at admission, and severe global developmental delay at 18 months of age. Fluorescence in situ hybridization findings confirmed that the deleted regions contained at least 15q22. The chromosome analysis revealed a karyotype of 46,XY,del(15) (q22q23). Parental chromosome analysis was performed and results were normal. After reviewing the limited literature on interstitial 15q deletions, we believe that the presented case is the first description of mapping of an interstitial deletion involving the chromosome 15q22q23 segment in Korea. This report adds to the knowledge of the clinical phenotype associated with the 15q22q23 deletion.

Overlapping microdeletions involving 15q22.2 narrow the critical region for intellectual disability to NARG2 and RORA

Microdeletions in the 15q22 region have not been well documented. We collected genotype and phenotype data from five patients with microdeletions involving 15q22.2, which were between 0.7 Mb and 6.5 Mb in size; two were of de novo origin and one was of familial origin. Intellectual disability and epilepsy are frequently observed in patients with 15q22.2 deletions. Genotype-phenotype correlation analysis narrowed the critical region for such neurologic symptoms to a genomic region of 654 Kb including the NMDA receptor-regulated 2 gene (NARG2) and the PAR-related orphan receptor A gene (RORA), either of which may be responsible for neurological symptoms commonly observed in patients with deletions in this region. The neighboring regions, including the forkhead box B1 gene (FOXB1), may also be related to the additional neurological features observed in the patients with larger deletions.

Knockout of G protein β5 impairs brain development and causes multiple neurologic abnormalities in mice

Gβ5 is a divergent member of the signal-transducing G protein β subunit family encoded by GNB5 and expressed principally in brain and neuronal tissue. Among heterotrimeric Gβ isoforms, Gβ5 is unique in its ability to heterodimerize with members of the R7 subfamily of the regulator of G protein signaling proteins that contain G protein-γ like domains. Previous studies employing Gnb5 knockout (KO) mice have shown that Gβ5 is an essential stabilizer of such regulator of G protein signaling proteins and regulates the deactivation of retinal phototransduction and the proper functioning of retinal bipolar cells. However, little is known of the function of Gβ5 in the brain outside the visual system. We show here that mice lacking Gβ5 have a markedly abnormal neurologic phenotype that includes impaired development, tiptoe-walking, motor learning and coordination deficiencies, and hyperactivity. We further show that Gβ5-deficient mice have abnormalities of neuronal development in cerebellum and hippocampus. We find that the expression of both mRNA and protein from multiple neuronal genes is dysregulated in Gnb5 KO mice. Taken together with previous observations from Gnb5 KO mice, our findings suggest a model in which Gβ5 regulates dendritic arborization and/or synapse formation during development, in part by effects on gene expression.

The clinical spectrum of complete FBN1 allele deletions

The most common mutations found in FBN1 are missense mutations (56%), mainly substituting or creating a cysteine in a cbEGF domain. Other mutations are frameshift, splice and nonsense mutations. There are only a few reports of patients with marfanoid features and a molecularly proven complete deletion of a FBN1 allele. We describe the clinical features of 10 patients with a complete FBN1 gene deletion. Seven patients fulfilled the Ghent criteria for Marfan syndrome (MFS). The other three patients were examined at a young age and did not (yet) present the full clinical picture of MFS yet. Ectopia lentis was present in at least two patients. Aortic root dilatation was present in 6 of the 10 patients. In three patients, the aortic root diameter was on the 95th percentile and in one patient, the diameter of the aortic root was normal, the cross-section, however, had a cloverleaf appearance. Two patients underwent aortic root surgery at a relatively young age (27 and 34 years). Mitral valve prolapse was present in 4 of the 10 patients, and billowing of the mitral valve in 1. All patients had facial and skeletal features of MFS. Two patients with a large deletion extending beyond the FBN1 gene had an extended phenotype. We conclude that complete loss of one FBN1 allele does not predict a mild phenotype, and these findings support the hypothesis that true haploinsufficiency can lead to the classical phenotype of Marfan syndrome.

Phenotype-genotype correlation of a patient with a "balanced" translocation 9;15 and cryptic 9q34 duplication and 15q21q25 deletion

We report on a 2-year-old boy with intellectual disabilities, distinctive facies, hypotonia, cardiac, and renal malformations. During his infancy he had recurrent episodes of apnea, cyanosis, and bradycardia. Chromosomal analysis showed a de novo apparently balanced translocation 46,XY,t(9;15)(q31;q26)dn. The use of array-comparative genomic hybridization (CGH) however, revealed the presence of additional cryptic complex chromosomal rearrangements involving a approximately 5-5.8 Mb distal duplication on chromosome 9 (9q34.1 --> 9q34.3), and deletions on three separate regions of chromosome 15 adding to approximately 8.1-12.2 Mb (15q21.2 --> 15q21.3, 15q22.31 --> 15q23, 15q25.1 --> 15q25.2). During confirmation with fluorescence in situ hybridization (FISH) an inversion was unexpectedly revealed on chromosome 15 (15q21.1 --> 15q21.2). To our knowledge this is the first patient reported whose phenotype is due to partial trisomy 9q, and complex interstitial deletions of 15q, not involving the Prader-Willi/Angelman region and encompassing the critical region 15q21q25. We provide correlation between the clinical findings of our patient and the phenotype of the 9q34 duplication syndrome, the 15q21, and the 15q25 deletion syndromes.

Gene copy number variations in Asian patients with congenital bilateral absence of the vas deferens

BACKGROUND

Congenital bilateral absence of the vas deferens (CBAVD) is a distinct clinical entity accounting for approximately 25% of obstructive azoospermia in infertile men. The association between CBAVD and mutated CFTR (cystic fibrosis transmembrane conductance regulator) alleles is well demonstrated in Caucasians, but the identity of CBAVD-susceptibility genes remains elusive in Asians. We investigate genomic copy number variations (CNVs) in a patient cohort of Taiwan.

METHODS AND RESULTS

Genome-wide screening for genetic CNVs was conducted on eight individuals with CBAVD using array-based comparative genomic hybridization. One recurrent CNV was detected on 3q26.1 in five patients, and another was detected on a reproduction-related gene PANK2 in two patients. For the former, we further characterized the breakpoints in CBAVD and assessed the incidence in healthy individuals by tiling path arrays. The deletion in each patient was confirmed, and seven out of the eight controls were also affected. Examination of the homozygous loss of PANK2 by PCR in a larger cohort showed a homozygous deletion in only one of the 26 CBAVD males, and not in any of the 20 azoospermic patients without CBAVD, nor in any of the 16 control subjects.

CONCLUSIONS

Our results suggest that 3q26.1 may not be a critical region for CBAVD. Additionally no strong association was found for PANK2 in this reproduction disorder. Other reproduction-related genes, such as PBX1, BRD3, COL18A1 and HMOX1, identified by this initial study may inspire further investigation.

Mild mental retardation in a child with a de novo interstitial deletion of 15q21.2q22.1: a comparison with previously described cases

We report on a child with mild mental retardation, hypotelorism, blepharophimosis, face slight asymmetry and partial hypoplasia of corpus callosum, with an interstitial deletion of a chromosome 15. The deletion was molecularly characterized by array-CGH and FISH techniques. This rearrangement has a 7.18Mb extension and maps to 15q21.2q22.1. To date, there have been only six individuals reported with a deletion of 15q21; in three cases, the rearrangement was characterized by molecular cytogenetic techniques. After a comparison with these three cases, it appeared that the deletion we found is one of the smallest and it overlaps the distal portion of the ones taken into account. Finally, we tried to delineate the genotype-phenotype correlation in patients with a deletion of 15q21.

Craniosynostosis in a patient with a de novo 15q15-q22 deletion

Interstitial deletions involving the chromosomal band 15q15 are very rare. A total of five cases were previously reported. Here another case of a 15q15.2-q22.2 deletion is reported, presenting with severe craniosynostosis of coronary, metopic, and sagittal sutures. The chromosome 15 with the 17.7-Mb deletion was of the paternal origin. A critical region for craniosynostosis may be located at the 734-kb segment at 15q15.2. Interestingly, the entire FBN1 gene was deleted in this patient.

Large genomic fibrillin-1 (FBN1) gene deletions provide evidence for true haploinsufficiency in Marfan syndrome

Mutations in the FBN1 gene are the major cause of Marfan syndrome (MFS), an autosomal dominant connective tissue disorder, which displays variable manifestations in the cardiovascular, ocular, and skeletal systems. Current molecular genetic testing of FBN1 may miss mutations in the promoter region or in other noncoding sequences as well as partial or complete gene deletions and duplications. In this study, we tested for copy number variations by successively applying multiplex ligation-dependent probe amplification (MLPA) and the Affymetrix Human Mapping 500 K Array Set, which contains probes for approximately 500,000 single-nucleotide polymorphisms (SNPs) across the genome. By analyzing genomic DNA of 101 unrelated individuals with MFS or related phenotypes in whom standard genetic testing detected no mutation, we identified FBN1 deletions in two patients with MFS. Our high-resolution approach narrowed down the deletion breakpoints. Subsequent sequencing of the junctional fragments revealed the deletion sizes of 26,887 and 302,580 bp, respectively. Surprisingly, both deletions affect the putative regulatory and promoter region of the FBN1 gene, strongly indicating that they abolish transcription of the deleted allele. This expectation of complete loss of function of one allele, i.e. true haploinsufficiency, was confirmed by transcript analyses. Our findings not only emphasize the importance of screening for large genomic rearrangements in comprehensive genetic testing of FBN1 but, importantly, also extend the molecular etiology of MFS by providing hitherto unreported evidence that true haploinsufficiency is sufficient to cause MFS.

Coarctation of the aorta and mild to moderate developmental delay in a child with a de novo deletion of chromosome 15(q21.1q22.2)

Background

Deletion of 15q21q22 is a rare chromosomal anomaly. To date, there have been nine reports describing ten individuals with different segmental losses involving 15q21 and 15q22. Many of these individuals have common features of growth retardation, hypotonia and moderate to severe mental retardation. Congenital heart disease has been described in three individuals with interstitial deletion involving this region of chromosome 15.

Case presentation

We report a child with coarctation of the aorta, partial agenesis of corpus callosum and mild to moderate developmental delay, with a de novo deletion of 15q21.1q22.2, detected by the array Comparative Genomic Hybridization (CGH). We utilized chromosome 15-specific microarray-based CGH to define the chromosomal breakpoints in this patient.

Conclusion

This is the first description of mapping of an interstitial deletion involving the chromosome 15q21q22 segment using the chromosome 15-specific array-CGH. The report also expands the spectrum of clinical phenotype associated with 15q21q22 deletion.