Guideline recommendations for diagnosis and clinical management of Ring14 syndrome-first report of an ad hoc task force

The past, present, and future for constitutional ring chromosomes: A report of the international consortium for human ring chromosomes

Human ring chromosomes (RCs) are rare diseases with an estimated newborn incidence of 1/50,000 and an annual occurrence of 2,800 patients globally. Over the past 60 years, banding cytogenetics, fluorescence in situ hybridization (FISH), chromosome microarray analysis (CMA), and whole-genome sequencing (WGS) has been used to detect an RC and further characterize its genomic alterations. Ring syndrome featuring sever growth retardation and variable intellectual disability has been considered as general clinical presentations for all RCs due to the cellular losses from the dynamic mosaicism of RC instability through mitosis. Cytogenomic heterogeneity ranging from simple complete RCs to complex rearranged RCs and variable RC intolerance with different relative frequencies have been observed. Clinical heterogeneity, including chromosome-specific deletion and duplication syndromes, gene-related organ and tissue defects, cancer predisposition to different types of tumors, and reproductive failure, has been reported in the literature. However, the patients with RCs reported in the literature accounted for less than 1% of its occurrence. Current diagnostic practice lacks laboratory standards for analyzing cellular behavior and genomic imbalances of RCs to evaluate the compound effects on patients. Under-representation of clinical cases and lack of comprehensive diagnostic analysis make it a challenge for evidence-based interpretation of clinico-cytogenomic correlations and recommendation of follow-up clinical management. Given recent advancements in genomic technologies and organized efforts by international collaborations and patient advocacy organizations, the prospective of standardized cytogenomic diagnosis and evidence-based clinical management for all patients with RCs could be achieved at an unprecedented global scale.

North Carolina macular dystrophy shows a particular drusen phenotype and atrophy progression

BACKGROUND/AIM

To provide a comprehensive multimodal retinal imaging characterisation of patients with North Carolina macular dystrophy (NCMD).

METHODS

Clinical evaluation and retinal imaging in six families.

RESULTS

Twenty-one subjects showed phenotypic characteristics of NCMD . Small drusen-like deposits were found in all affected individuals, either tightly grouped in the macula, or surrounding atrophic or fibrotic macular alterations. These small subretinal lesions showed an increased fundus autofluorescence and were associated with only mild irregularities on optical coherence tomography imaging. Similar drusen-like deposits were regularly seen in the peripheral fundus, predominantly temporally and often with a radial distribution. Two patients showed a bilateral chorioretinal atrophy and two had a macular neovascularisation (MNV). Findings from follow-up examinations were available from 11 patients. The retinal phenotype remained overall stable, except for two patients: one patient with atrophy showed a distinct growth of the atrophic lesions on longitudinal AF imaging over a review period of 14 years. One patient with MNV showed a unilateral decline of best-corrected visual acuity. Genetic testing identified the single nucleotide variant chr6:100040987G>C upstream of the PRDM13 gene in all family members with NCMD phenotype.

CONCLUSION

Patients with NCMD show a characteristic retinal phenotype and distribution of drusen that differ from drusen in patients with age-related macular degeneration. Although the prognosis of this developmental condition is overall better than for other macular diseases with drusen, patients may be at risk of developing MNV or enlargement of pre-existing atrophy.

Ring Chromosome 20 Syndrome: Genetics, Clinical Characteristics, and Overlapping Phenotypes

Ring chromosome 20 [r(20)] syndrome is a rare condition characterized by a non-supernumerary ring chromosome 20 replacing a normal chromosome 20. It is commonly seen in a mosaic state and is diagnosed by means of karyotyping. r(20) syndrome is characterized by a recognizable epileptic phenotype with typical EEG pattern, intellectual disability manifesting after seizure onset in otherwise normally developing children, and behavioral changes. Despite the distinctive phenotype, many patients still lack a diagnosis-especially in the genomic era-and the pathomechanisms of ring formation are poorly understood. In this review we address the genetic and clinical aspects of r(20) syndrome, and discuss differential diagnoses and overlapping phenotypes, providing the reader with useful tools for clinical and laboratory practice. We also discuss the current issues in understanding the mechanisms through which ring 20 chromosome causes the typical manifestations, and present unpublished data about methylation studies. Ultimately, we explore future perspectives of r(20) research. Our intended audience is clinical and laboratory geneticists, child and adult neurologists, and genetic counselors.

Chromosome 14 deletions, rings, and epilepsy genes: A riddle wrapped in a mystery inside an enigma

The ring 14 syndrome is a rare condition caused by the rearrangement of one chromosome 14 into a ring-like structure. The formation of the ring requires two breakpoints and loss of material from the short and long arms of the chromosome. Like many other chromosome syndromes, it is characterized by multiple congenital anomalies and developmental delays. Typical of the condition are retinal anomalies and drug-resistant epilepsy. These latter manifestations are not found in individuals who are carriers of comparable 14q deletions without formation of a ring (linear deletions). To find an explanation for this apparent discrepancy and gain insight into the mechanisms leading to seizures, we reviewed and compared literature cases of both ring and linear deletion syndrome with respect to both their clinical manifestations and the role and function of potentially epileptogenic genes. Knowledge of the epilepsy-related genes in chromosome 14 is an important premise for the search of new and effective drugs to combat seizures. Current clinical and molecular evidence is not sufficient to explain the known discrepancies between ring and linear deletions.

Multimodal imaging of ring 14 syndrome associated maculopathy

Background: Ring 14 syndrome is a rare chromosomal disorder characterized by a ring-shaped appearance of chromosome 14. Classically findings include distinct facial characteristics, refractory epilepsy, global development delay, muscular hypotonia and ocular abnormalities. Here we report a retinal multimodal imaging analyses of a ring chromosome 14 syndrome patient with associated macular pigmentary changes.Materials and Methods: Case report of an 11-year-old female with a history of refractory epilepsy since 3 months of age was diagnosed with ring 14 syndrome after karyotype at 8 months old. She presented with muscle weakness, mild intellectual delay, associated hyperopia and punctiform yellowish lesions. Multimodal imaging including fundus photography, red-free fundus photography, fundus auto-fluorescence and spectral-domain optical coherence tomography were used to assess this patient.Results: An 11-year-old female with ring 14 syndrome caused by the fusion of terminal breakpoints in both the short arm and long arm of chromosome 14 at p11.1 and q32.3, respectively. At eye exam, the best corrected visual acuity was 20/20 at both eyes with associated hyperopia. Macula showing scattered punctiform yellowish lesions, bright on red-free fundus photography and hyperautofluorescence dots in the same area. The SD-OCT showed normal characteristics at both eyes with the exception of localized irregularity of the RPE in an area associated with a macular yellow dots.Conclusions: Ring 14 syndrome can cause hyperopia and associated macular yellow dots visible at multimodal imaging analyses. Our data support regular eye examination for all patients with ring chromosome 14 syndrome.

Human ring chromosome registry for cases in the Chinese population: re-emphasizing Cytogenomic and clinical heterogeneity and reviewing diagnostic and treatment strategies

BACKGROUND

Constitutional ring chromosomes are rare orphan chromosomal disorders. Ring chromosome syndrome featuring growth retardation and mild to intermediate intellectual disability is likely caused by the dynamic behavior of ring chromosome through cell cycles. Chromosomal and regional specific phenotypes likely result from segmental losses and gains during the ring formation. Although recent applications of genomic copy number and sequencing analyses revealed various ring chromosome structures from an increasing number of case studies, there was no organized effort for compilating and curating cytogenomic and clinical finding for ring chromosomes.

METHODS

A web-based interactive 'Human Ring Chromosome Registry' using Microsoft Access based relational database was developed to present genetic and phenotypic findings of ring chromosome cases. Chinese ring chromosome cases reported in the literature was reviewed and compiled as a testing data set to validate this registry.

RESULTS

A total of 113 cases of ring chromosomes were retrieved in all chromosomes except for chromosomes 16, 17 and 19. The most frequently seen ring chromosomes by a decreasing order of relative frequencies were ring 13 (14%), X (12%), 22 (10%), 15 (9%), 14 (7%), and 18 (7%). Genomic imbalances were detected in 18 out of 19 cases analyzed by microarray or sequencing. Variable clinical manifestations of developmental delay, dysmorphic facial features, intellectual disability, microcephaly, and hypotonia were noted in most autosomal rings. Chromosomal specific syndromic phenotypes included Wolf-Hirschhorn syndrome in a ring chromosome 4, cri-du-chat syndrome in a ring chromosome 5, epilepsy in ring chromosomes 14 and 20, Turner syndrome in ring chromosome X, and infertility in ring chromosomes 13, 21, 22 and Y. Effective growth hormone supplemental treatment for growth retardation in a ring chromosome 18 was noted.

CONCLUSIONS

Based on findings from these Chinese ring chromosome cases, guidelines for cytogenomic diagnosis and criteria for case registration were proposed. Further research to define underlying mechanisms of ring chromosome formation and dynamic mosaicism, to delineate the genotype-phenotype correlations, and to develop chromosome therapy for ring chromosomes were discussed.

Chromothripsis and ring chromosome 22: a paradigm of genomic complexity in the Phelan-McDermid syndrome (22q13 deletion syndrome)

Introduction

Phelan-McDermid syndrome (PMS) is caused by SHANK3 haploinsufficiency. Its wide phenotypic variation is attributed partly to the type and size of 22q13 genomic lesion (deletion, unbalanced translocation, ring chromosome), partly to additional undefined factors. We investigated a child with severe global neurodevelopmental delay (NDD) compatible with her distal 22q13 deletion, complicated by bilateral perisylvian polymicrogyria (BPP) and urticarial rashes, unreported in PMS.

Methods

Following the cytogenetic and array-comparative genomic hybridization (CGH) detection of a r(22) with SHANK3 deletion and two upstream duplications, whole-genome sequencing (WGS) in blood and whole-exome sequencing (WES) in blood and saliva were performed to highlight potential chromothripsis/chromoanagenesis events and any possible BPP-associated variants, even in low-level mosaicism.

Results

WGS confirmed the deletion and highlighted inversion and displaced order of eight fragments, three of them duplicated. The microhomology-mediated insertion of partial Alu-elements at one breakpoint junction disrupted the topological associating domain joining NFAM1 to the transcriptional coregulator TCF20. WES failed to detect BPP-associated variants.

Conclusions

Although we were unable to highlight the molecular basis of BPP, our data suggest that SHANK3 haploinsufficiency and TCF20 misregulation, both associated with intellectual disability, contributed to the patient’s NDD, while NFAM1 interruption likely caused her skin rashes, as previously reported. We provide the first example of chromoanasynthesis in a constitutional ring chromosome and reinforce the growing evidence that chromosomal rearrangements may be more complex than estimated by conventional diagnostic approaches and affect the phenotype by global alteration of the topological chromatin organisation rather than simply by deletion or duplication of dosage-sensitive genes.