Department of Dermatology, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
Institute of Dermatology, Shanghai Jiaotong University School of Medicine, Shanghai, China
Instrumental Analysis Center, Shanghai Jiao Tong University, Shanghai, China
NHC Key Laboratory of Glycoconjugate Research, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Fudan University, Shanghai, China
These authors contributed equally
Background: Severe dermatitis, multiple allergies and metabolic wasting (SAM) syndrome comprise a rare genodermatosis associated with biallelic (homozygous or compound heterozygous) mutations in the DSG1 (desmoglein-1) gene, or heterozygous mutations in the DSP (desmoplakin) gene. To date, while many patients with SAM syndrome have been described, the number of cases with SAM syndrome with deep-intronic variants, together its genetic aetiology, remain limited. Objective: We report the case of a five-year-old Chinese boy with atypical SAM syndrome. Materials & Methods: Relevant blood specimens from the family were collected. DNA isolation, RNA isolation and cDNA synthesis, and next-generation sequencing using a multi-gene panel were applied to verify the pathogenic gene. To test the functional consequences and pathogenic mechanism of the deep-intronic mutation in vitro, a mini gene strategy was constructed. Results: A heterozygous DSG1 deletion (c.2437_2450delACCTATCCCTCGGG: p.Tyr814Trpfs*6) and a deep-intronic (c.1688-30A > T) variant were identified. The identified intronic variant was shown to create an alternative splice site, leading to nonsense-mediated mRNA decay of the aberrant transcript. Conclusion: This is the first study to demonstrate a causal role for a deep-intronic DSG1 mutation in a patient with SAM syndrome. Our findings underline the need to analyse the intronic regions of DSG1 in patients with SAM syndrome. Improved diagnosis and a better understanding of prognosis will lead to clearer a picture of the concept of atypical SAM syndrome.