The Chromosome 18 Clinical Resource Center

Mosaic chromosome 18 anomaly delineated in a child with dysmorphism using a three-pronged cytogenetic techniques approach: a case report

Background

A plethora of cases are reported in the literature with iso- and ring-chromosome 18. However, co-occurrence of these two abnormalities in an individual along with a third cell line and absence of numerical anomaly is extremely rare.

Case presentation

A 7-year-old female was referred for diagnosis due to gross facial dysmorphism and severe developmental delay. She presented with dysmorphic features, hypo/hyper pigmentation of the skin, intellectual disability and craniosynostosis. G-banding chromosome analysis suggested mos 46,XX,psu idic(18)(p11.2)[25]/46,XX,r(?18)[30]. Additional analysis by molecular karyotyping suggested pure partial deletion of 15 Mb on 18p (18p11.32p11.21). Lastly, multiple rearrangements and detection of a third cell line (ring chr18 and interstitial deletion) of chr18 was observed by multi-color banding.

Conclusion

The current study presents a novel case of chromosomal abnormalities pertaining to chromosome 18 across 3 cell lines, which were delineated with a combinatorial approach of diagnostic methods.

The Consequences of Abnormal Gene Dosage: Lessons from Chromosome 18

Accurate interpretation of genomic copy number variation (CNV) remains a challenge and has important consequences for both congenital and late-onset disease. Hemizygosity dosage characterization of the genes on chromosome 18 reveals a spectrum of outcomes ranging from no clinical effect, to risk factors for disease, to both low- and high-penetrance disease. These data are important for accurate and predictive clinical management. Additionally, the potential mechanisms of reduced penetrance due to dosage compensation are discussed as a key to understanding avenues for potential treatment. This review describes the chromosome 18 findings, and discusses the molecular mechanisms that allow haploinsufficiency, reduced penetrance, and dosage compensation.

The Chromosome 18 Clinical Resource Center

BACKGROUND

The Chromosome 18 Clinical Research Center has created a pediatrician-friendly virtual resource center for managing patients with chromosome 18 abnormalities. To date, children with rare chromosome abnormalities have been cared for either symptomatically or palliatively as a reaction to the presenting medical problems. As we enter an era of genomic-informed medicine, we can provide children, even those with individually unique chromosome abnormalities, with proactive medical care and management based on the most contemporary data on their specific genomic change. It is problematic for practicing physicians to obtain and use the emerging data on specific genes because this information is derived from diverse sources (e.g., animal studies, case reports, in vitro explorations) and is often published in sources that are not easily accessible in the clinical setting.

METHODS

The Chromosome 18 Clinical Resource Center remedies this challenging problem by curating and synthesizing the data with clinical implications. The data are collected from our database of over 26 years of natural history and medical data from over 650 individuals with chromosome 18 abnormalities.

RESULTS

The resulting management guides and video presentations are a first edition of this collated data specifically oriented to guide clinicians toward the optimization of care for each child.

CONCLUSION

The chromosome 18 data and guides also serve as models for an approach to the management of any individual with a rare chromosome abnormality of which there are over 1,300 born every year in the US alone.