Charakterystyka kliniczna i genetyczna zespołu Angelmana w chińskiej kohorcie pacjentów: rozszerzenie spektrum wariantów genu UBE3A i zastosowanie sekwencjonowania długich odczytów

Abstract Background: Angelman syndrome (AS) is a neurogenetic disorder characterized by intellectual disability and epileptic seizures, primarily caused by dysfunction of the maternal UBE3A gene in the 15q11.2 region. The genetic etiology is heterogeneous, including maternal 15q11-q13 deletions, paternal uniparental disomy (UPD) of chromosome 15, maternal pathogenic UBE3A variants, or imprinting defects. This diversity necessitates comprehensive diagnostic approaches, posing challenges for precise diagnosis and genetic counseling. Methods: Clinically suspected AS patients were recruited, and their clinical and genetic data were analyzed. Multiple genetic testing methods were employed, including methylation-specific MLPA (MS-MLPA), trio-based whole-exome sequencing (WES), whole-genome sequencing (WGS), SNP-array and copy number variation sequencing (CNV-seq). Long-range PCR (LR-PCR), PacBio Sequel series Single Molecule Real-Time (SMRT) sequencing technology and Blocker displacement amplification (BDA) were used to determine parental allele origin and detect low-level mosaicism. Results: Thirteen patients were included. All exhibited moderate to severe developmental delay, six had epilepsy with characteristic EEG findings. Ataxia, frequent smiling and laughter, microcephaly and dysmorphism were observed in 5, 4, 2, and 2 cases, respectively. Brain MRI findings were either normal or showed nonspecific abnormalities. Genetic analysis identified UBE3A heterozygous variants (8 cases), 15q11-q13 deletions (4 cases) and paternal UPD (1 case). Three novel variants in UBE3A (c.409T > G p. (Cys137Gly), c.2038_2042del p. (Ser680fs), c.2510C > T p. (Ser837Phe)) have not been reported before. Notably, two siblings harbored the same UBE3A variant (c.409T > C p. (Cys137Arg)) undetectable in parental blood; PacBio sequencing confirmed parental allele origin. Negative BDA result suggests the mosaic mother either does not harbor this variant or this variant exists in the assessed somatic samples but at a level lower than 5‰. Conclusions: This study summarizes characteristics of 13 Chinese patients with AS, expanding the clinical and genetic spectrum of AS. It reveals the genetic heterogeneity of AS, emphasizing the necessity of multimodal testing for accurate diagnosis. Long-read sequencing enhances parental origin determination, and germline mosaicism underscores the need for prenatal counseling.