When Neurodevelopment Meets Autoimmunity: Pemphigus Foliaceus in Rett Syndrome Expands the Clinical Spectrum—A Case Report

Rett syndrome (RTT, OMIM 312750) is a complex multisystem neurodevelopmental disorder. Evidence suggests that RTT may have an autoimmune component and inflammatory activation. However, the autoimmune manifestations remain poorly described. Pemphigus foliaceus is a debilitating autoimmune blistering condition caused by IgG autoantibodies that target desmoglein-1 (Dsg1), resulting in widespread skin blistering and lesions. We report a case of pemphigus foliaceus in a 20-year-old female with RTT and discuss its clinical implications. Clinical data obtained from electronic health records were extracted and reviewed. Genetic testing was performed to identify the specific methyl-CpG-binding protein 2 (MECP2) mutation and on an expanded panel of 55 genes associated with pemphigus foliaceus and related blistering disorders. The individual had pemphigus foliaceus, which required immunosuppression, intravenous immunoglobulin (IVIg) therapy, and Rituximab. The disease trajectory was complicated by infections, aspiration pneumonia, and hypoxic cardiac arrest. There was progressive functional decline, and disease control was difficult to achieve, with frequent flares. Genetic testing confirmed a heterozygous pathogenic MECP2 variant (NM_001110792.1:c.952C>T; p.(Arg318Cys)). HLA genotyping identified alleles consistent with the HLA-DRB1*04:02–HLA-DQA1*03:01–HLA-DQB1*03:02 (DR4/DQ8) haplotype. Furthermore, genetic analysis identified a heterozygous DSG1 variant rs12967407. This study reports the first case of pemphigus foliaceus in RTT, expanding the clinical spectrum of RTT beyond its neurodevelopmental phenotype. The DR4/DQ8 haplotype, previously associated with pemphigus susceptibility, supports a background of genetic susceptibility in this individual. No causal association between RTT and pemphigus foliaceus can be inferred from this single case. Rather, this case demonstrates that a rare autoimmune disorder such as pemphigus foliaceus can co-occur with a pathogenic MECP2 mutation. The coexistence of a genetic and autoimmune disease can result in a more complex clinical presentation and treatment course. The case further emphasises the need for increased vigilance in identifying new and emerging systemic pathology alongside RTT.