Clinical and genomic profiling of a patient with a de novo ring chromosome 18: a case report highlighting autoimmune and neurological implications.

Ring chromosome 18 (r(18)) is a rare chromosomal abnormality characterized by the circular rearrangement of chromosome 18, which presents significant challenges in genotype-phenotype correlations due to variability in deletions across the 18p and 18q arms. We report the case of a pediatric patient with a de novo ring chromosome 18, diagnosed by karyotype analysis and confirmed by high-resolution SNP arrays. The patient exhibited pathogenic copy number variants (CNVs) in the 18p11.32p11.22 and 18q23 regions, involving 36 and 10 OMIM genes, respectively. Clinically, the patient presented with hypothyroidism secondary to autoimmune thyroiditis, autoimmune hepatitis type II, and genetic predisposition to celiac disease and insulin-dependent diabetes mellitus (IDDM) along with notable dysmorphic features. The 18q microdeletion encompasses the MBP gene, involved in the development and functionality of the nervous system, as supported by hypotonia and gliosis shown by the MRI. This case highlights the complex interplay between genetic imbalances on chromosome 18 and autoimmune phenotypes, emphasizing the need for ongoing research to elucidate underlying mechanisms and optimize clinical management for individuals with r(18).