18p Deletion Syndrome Associated with Type 1 Diabetes and Hashimoto’s Thyroiditis: A Case Report on Autoimmune Disorders and Genetic Factors

18p deletion syndrome is a rare chromosomal disorder that can present with a wide range of phenotypic features and is occasionally associated with autoimmune diseases. We report the case of a 3-year and 8-month-old girl who presented with polydipsia and polyuria and was subsequently diagnosed with type 1 diabetes mellitus (T1DM) based on clinical and laboratory findings. The patient exhibited dysmorphic facial features and developmental delay, leading to genetic testing, which revealed a 13.7 Mb deletion on the short arm of chromosome 18 (18p11.32p11.21). Over the following years, she developed additional features, including Hashimoto's thyroiditis, epilepsy, subaortic stenosis requiring surgical resection, IgA deficiency, bilateral sensorineural hearing loss, and myopia. Genetic analysis also identified the deletion of several potentially disease-modifying genes, including PTPN2, PTPRM, LPIN2, USP14, and ADCYAP1. This case highlights the potential role of genes within the 18p region in the pathogenesis of autoimmune endocrinopathies. It supports further investigation into the immunogenetic mechanisms in 18p deletion syndrome.