Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects

Congenital anterior segment ocular disorders: Genotype-phenotype correlations and emerging novel mechanisms

Development of the anterior segment of the eye requires reciprocal sequential interactions between the arising tissues, facilitated by numerous genetic factors. Disruption of any of these processes results in congenital anomalies in the affected tissue(s) leading to anterior segment disorders (ASD) including aniridia, Axenfeld-Rieger anomaly, congenital corneal opacities (Peters anomaly, cornea plana, congenital primary aphakia), and primary congenital glaucoma. Current understanding of the genetic factors involved in ASD remains incomplete, with approximately 50% overall receiving a genetic diagnosis. While some genes are strongly associated with a specific clinical diagnosis, the majority of known factors are linked with highly variable phenotypic presentations, with pathogenic variants in FOXC1, CYP1B1, and PITX2 associated with the broadest spectrum of ASD conditions. This review discusses typical clinical presentations including associated systemic features of various forms of ASD; the latest functional data and genotype-phenotype correlations related to 25 ASD factors including newly identified genes; promising novel candidates; and current and emerging treatments for these complex conditions. Recent developments of interest in the genetics of ASD include identification of phenotypic expansions for several factors, discovery of multiple modes of inheritance for some genes, and novel mechanisms including a growing number of non-coding variants and alleles affecting specific domains/residues and requiring further studies.

Prenatal diagnosis of chromosome 18 long arm deletion syndrome by high-throughput sequencing: Two case reports

RATIONALE

Chromosome 18 long arm deletion syndrome is a group of clinical syndromes caused by partial or total genetic material deletion of the long arm of chromosome 18 (18q), whose clinical manifestations are related to presentation and developmental abnormalities in various aspects such as intelligence, face, and movement. Prenatal diagnosis of this syndrome is challenging because of its low incidence and uncharacteristic prenatal clinical performance. In this paper, 2 cases of partial deletion of 18q found in prenatal amniotic fluid examination by high-throughput sequencing were reported and analyzed.

PATIENT CONCERNS

In patient 1, non-invasive prenatal gene detection at 21 + 2 weeks of gestation suggests a risk of trisomy 18. In patient 2, ultrasound examination at 21 + 2 weeks of gestation revealed a single live fetus, but it was difficult to pinpoint whether the fetus had only 1 umbilical artery to supply blood.

DIAGNOSIS AND INTERVENTION

The 18q deletion syndrome was diagnosed by chromosome karyotype analysis and high-throughput sequencing.

OUTCOMES

The pregnancies were terminated due to the abnormal chromosome.

LESSON

This report adds novel variants to the genetic profile of 18q deletion, in order to enrich the genetic data of long arm deletion of 18 chromosomes and provide better services for pre-screening, diagnosis, and genetic counseling for this disease.

Clinical delineation of 18q11-q12 microdeletion: Intellectual disability, speech and behavioral disorders, and conotruncal heart defects

Background

Since the establishment of chromosomal microarrays in clinical practice, many new microdeletion/microduplication syndromes have been identified, including 18q11.2 microdeletion. Chromosome 18q deletion syndrome is commonly classified into distal deletion and a much rarer proximal interstitial deletion spanning the 18q11.2‐q21.1 region.

Methods

We report two new patients and review 27 additional cases in DECIPHER/ClinGen databases and four cases from the literature, with more proximal 18q deletions involving 18q11‐q12 (band 1 only; 17.2–43.5 Mb position) deletion.

Results

Common presentations of 18q11‐q12 deletions include developmental delay/intellectual disability (DD/ID) (82%); speech delay/autism/attention deficit and hyperactivity/other behavioral problems (30%); conotruncal heart defects (15%); and subtle/non‐specific facial dysmorphism. The deletion in four out of five cases with cardiac defect was distal to GATA6, suggesting an alternative mechanism other than haploinsufficiency of GATA6 as an underlying cause of cardiac malformations. Precocious puberty with advanced skeletal age was first observed in one patient, suggesting a unique and expanded phenotype of proximal 18q deletion. When comparing genotype–phenotype correlations from the present study with previous reports, the critical regions for selected phenotypes of 18q11‐q12 deletion syndrome could be narrowed down as follows: 38.8–43.5 Mb for moderate to severe DD/ID, 19.6–24.4 Mb and 26.9–28.6 Mb for conotruncal heart defect.

Conclusion

The detailed clinical delineation of the proximal 18q deletions identified in this study should contribute to better understanding of the genotype–phenotype correlations and better long‐term care of patients with this rare syndrome.