Inspired by a patient
Abstract
Background: Xia-Gibbs syndrome (XGS) is a rare neurodevelopmental disorder caused by pathogenic variants in the AT-hook DNA binding motif containing 1 (AHDC1) gene. More than 100 patients with XGS have been reported. In this study, we describe the findings from a Japanese cohort of patients with XGS. To enhance understanding, we also conducted a systematic literature review of XGS.
Methods: We collected clinical and genetic information from seven new Japanese patients with XGS which were diagnosed through comprehensive genetic analysis. A systematic literature review was also conducted using PubMed.
Results: All Japanese patients carried premature truncation variants or deletions. The core clinical features were global developmental delay and hypotonia, which were consistent with those observed in the 106 previously reported patients identified in our literature review. In one patient with a frameshift variant, escape from nonsense-mediated mRNA decay was confirmed using the patient's sample.
Conclusion: The clinical and molecular profiles of Japanese patients with XGS were analyzed and compared with those of previously reported patients from other countries, confirming the consistent characteristics of XGS. This study provides direct evidence of nonsense-mediated mRNA decay escape. A comprehensive understanding of this expanding phenotype is crucial for accurate diagnosis and management.
Jiang N, Zhang L, Zheng Z, Du H, Chen S, Pan H. Phenotypic subtypes of Xia-Gibbs syndrome: a latent class analysis. Eur J Hum Genet. 2025 Dec;33(12):1558-1566. doi: 10.1038/s41431-024-01754-0. Epub 2024 Dec 9. Erratum in: Eur J Hum Genet. 2026 Jun;34(6):886-892. doi: 10.1038/s41431-025-01825-w. PMID: 39648204; PMCID: PMC12669642.
Abstract
Xia-Gibbs syndrome (XGS) is a rare neurodevelopmental disorder with considerable clinical heterogeneity. To further characterize the syndrome's heterogeneity, we applied latent class analysis (LCA) on reported cases to identify phenotypic subtypes. By searching PubMed, Embase, China National Knowledge Infrastructure and Wanfang databases from inception to February 2024, we enrolled 97 cases with nonsense, frameshift or missense variants in the AHDC1 gene. LCA was based on the following 6 phenotypes with moderate occurrence and low missingness: ataxia, seizure, autism, sleep apnea, short stature and scoliosis. After excluding cases with missing data on all LCA variables or with unmatched phenotype-genotype information, a total of 85 cases were selected for LCA. Models with 1-5 classes were compared based on Akaike Information Criterion, Bayesian Information Criterion, Sample-Size Adjusted BIC and entropy. We used multinomial logistic regression (MLR) analyses to investigate the phenotype-genotype association and potential predictors for class membership. LCA revealed 3 distinct classes labeled as Ataxia subtype (n = 11 [12.9%]), Sleep apnea & short stature subtype (n = 23 [27.1%]) and Neuropsychological subtype (n = 51 [60.0%]). The commonest Neuropsychological subtype was characterized by high estimated probabilities of seizure, ataxia and autism. By adjusting for sex, age and variant type, MLR showed no significant association between phenotypic subtype and variant position. Age and variant type were identified as predictors of class membership. The findings of this review offer novel insights for different presentations of XGS. It is possible to deliver targeted monitoring and treatment for each subtype in the early stage.
Romano F, Falco M, Cappuccio G, Brunetti-Pierri N, Lonardo F, Torella A, Digilio MC, Dentici ML, Alfieri P, Agolini E, Novelli A, Garavelli L, Accogli A; TUDP; Striano P, Scarano G, Nigro V, Scala M, Capra V. Genotype-phenotype spectrum and correlations in Xia-Gibbs syndrome: Report of five novel cases and literature review. Birth Defects Res. 2022 Aug 1;114(13):759-767. doi: 10.1002/bdr2.2058. Epub 2022 Jun 18. PMID: 35716097; PMCID: PMC9545659.
Abstract
Background: Xia-Gibbs syndrome (XGS) is a rare neurodevelopmental disorder caused by pathogenic variants in the AT-hook DNA-binding motif-containing 1 gene (AHDC1), encoding a protein with a crucial role in transcription and epigenetic regulation, axonogenesis, brain function, and neurodevelopment. AHDC1 variants possibly act through a dominant-negative mechanism and may interfere with DNA repair processes, leading to genome instability and impaired DNA translesion repair. Variants affecting residues closer to the N-terminal are thought to determine a milder phenotype with better cognitive performances. However, clean-cut genotype-phenotype correlations are still lacking.
Cases: In this study, we investigated five subjects with XGS in whom exome sequencing led to the identification of five novel de novo pathogenic variants in AHDC1. All variants were extremely rare and predicted to cause a loss of protein function. The phenotype of the reported patients included developmental delay, hypotonia, and distinctive facial dysmorphisms. Additionally, uncommon clinical features were observed, including congenital hypothyroidism and peculiar skeletal abnormalities.
Conclusions: In this study, we report uncommon XGS features associated with five novel truncating variants in AHDC, thus expanding the genotype and phenotypic spectrum of this complex condition. We also compared our cases to previously reported cases, discussing the current status of genotype-phenotype correlations in XGS.
Cinelli G, Della Vecchia S, Bergonzini P, Caramaschi E, Spezia E, Parenti C, Madeo SF, Lucaccioni L, Francesca C, Pugliese M, Raviglione F, Colonna C, Calabrese O, Stanghellini I, Marongiu MC, Biagioni E, Ferrari AR, Battini R, Iughetti L. Clinical, Behavioral and Neuroradiological Phenotype in an Italian Cohort of Patients With Xia Gibbs Syndrome: A Multicenter Cross-Sectional Study and Systematic Literature Review. Am J Med Genet A. 2026 Sep;200(9):2067-2079. doi: 10.1002/ajmg.a.70163. Epub 2026 Apr 30. PMID: 42059486.
Abstract
Heterozygous variants in the AHDC1 gene are associated with Xia Gibbs Syndrome (XGS), a genetic disorder with a highly variable phenotype. Cognitive impairment, motor delay, language delay, neonatal hypotonia, and sleep apnea are considered "cardinal" signs of the disease. In a multicenter cross-sectional study, we analyzed the genetic, epileptological, behavioral, and neuroradiological features of 15 patients with XGS harboring heterozygous variants in AHDC1. The phenotype of our patient cohort is almost overlapping with that already reported in the literature. Seizures begin between 2 and 9 years, while EEG is generally characterized by normal background activity with paroxysmal abnormalities in the posterior areas increased by sleep. We systematically analyzed brain imaging findings as the most frequent brain alteration: the thinning of the corpus callosum, followed by posterior fossa malformation and lateral ventricle morphology abnormalities. Regarding psychiatric disorders, we observed neurodevelopmental disorders such as ID, language disorders, Autism spectrum disorders (ASD), and ADHD in preschoolers, followed by a prevalence of externalizing problems during childhood and adolescence. Our study showed that epilepsy and brain anomalies are very common among XGS individuals. MRI changes are nonspecific, but their association with other clinical features of the syndrome can guide early diagnosis. EEG abnormalities are present in all epileptic patients in the temporal-occipital regions with the same characteristics, so we could hypothesize that these abnormalities could represent a recognizable EEG pattern of XGS. Behavioral disorders represent an important problem, and longitudinal evaluations are needed to improve the classification of the psychopathological spectrum in XGS.
Background: Xia-Gibbs syndrome (XGS) is a rare neurodevelopmental disorder caused by pathogenic variants in the AT-hook DNA binding motif containing 1 (AHDC1) gene. More than 100 patients with XGS have been reported. In this study, we describe the findings from a Japanese cohort of patients with XGS. To enhance understanding, we also conducted a systematic literature review of XGS.
Methods: We collected clinical and genetic information from seven new Japanese patients with XGS which were diagnosed through comprehensive genetic analysis. A systematic literature review was also conducted using PubMed.
Results: All Japanese patients carried premature truncation variants or deletions. The core clinical features were global developmental delay and hypotonia, which were consistent with those observed in the 106 previously reported patients identified in our literature review. In one patient with a frameshift variant, escape from nonsense-mediated mRNA decay was confirmed using the patient's sample.
Conclusion: The clinical and molecular profiles of Japanese patients with XGS were analyzed and compared with those of previously reported patients from other countries, confirming the consistent characteristics of XGS. This study provides direct evidence of nonsense-mediated mRNA decay escape. A comprehensive understanding of this expanding phenotype is crucial for accurate diagnosis and management.
Jiang N, Zhang L, Zheng Z, Du H, Chen S, Pan H. Phenotypic subtypes of Xia-Gibbs syndrome: a latent class analysis. Eur J Hum Genet. 2025 Dec;33(12):1558-1566. doi: 10.1038/s41431-024-01754-0. Epub 2024 Dec 9. Erratum in: Eur J Hum Genet. 2026 Jun;34(6):886-892. doi: 10.1038/s41431-025-01825-w. PMID: 39648204; PMCID: PMC12669642.
Abstract
Xia-Gibbs syndrome (XGS) is a rare neurodevelopmental disorder with considerable clinical heterogeneity. To further characterize the syndrome's heterogeneity, we applied latent class analysis (LCA) on reported cases to identify phenotypic subtypes. By searching PubMed, Embase, China National Knowledge Infrastructure and Wanfang databases from inception to February 2024, we enrolled 97 cases with nonsense, frameshift or missense variants in the AHDC1 gene. LCA was based on the following 6 phenotypes with moderate occurrence and low missingness: ataxia, seizure, autism, sleep apnea, short stature and scoliosis. After excluding cases with missing data on all LCA variables or with unmatched phenotype-genotype information, a total of 85 cases were selected for LCA. Models with 1-5 classes were compared based on Akaike Information Criterion, Bayesian Information Criterion, Sample-Size Adjusted BIC and entropy. We used multinomial logistic regression (MLR) analyses to investigate the phenotype-genotype association and potential predictors for class membership. LCA revealed 3 distinct classes labeled as Ataxia subtype (n = 11 [12.9%]), Sleep apnea & short stature subtype (n = 23 [27.1%]) and Neuropsychological subtype (n = 51 [60.0%]). The commonest Neuropsychological subtype was characterized by high estimated probabilities of seizure, ataxia and autism. By adjusting for sex, age and variant type, MLR showed no significant association between phenotypic subtype and variant position. Age and variant type were identified as predictors of class membership. The findings of this review offer novel insights for different presentations of XGS. It is possible to deliver targeted monitoring and treatment for each subtype in the early stage.
Romano F, Falco M, Cappuccio G, Brunetti-Pierri N, Lonardo F, Torella A, Digilio MC, Dentici ML, Alfieri P, Agolini E, Novelli A, Garavelli L, Accogli A; TUDP; Striano P, Scarano G, Nigro V, Scala M, Capra V. Genotype-phenotype spectrum and correlations in Xia-Gibbs syndrome: Report of five novel cases and literature review. Birth Defects Res. 2022 Aug 1;114(13):759-767. doi: 10.1002/bdr2.2058. Epub 2022 Jun 18. PMID: 35716097; PMCID: PMC9545659.
Abstract
Background: Xia-Gibbs syndrome (XGS) is a rare neurodevelopmental disorder caused by pathogenic variants in the AT-hook DNA-binding motif-containing 1 gene (AHDC1), encoding a protein with a crucial role in transcription and epigenetic regulation, axonogenesis, brain function, and neurodevelopment. AHDC1 variants possibly act through a dominant-negative mechanism and may interfere with DNA repair processes, leading to genome instability and impaired DNA translesion repair. Variants affecting residues closer to the N-terminal are thought to determine a milder phenotype with better cognitive performances. However, clean-cut genotype-phenotype correlations are still lacking.
Cases: In this study, we investigated five subjects with XGS in whom exome sequencing led to the identification of five novel de novo pathogenic variants in AHDC1. All variants were extremely rare and predicted to cause a loss of protein function. The phenotype of the reported patients included developmental delay, hypotonia, and distinctive facial dysmorphisms. Additionally, uncommon clinical features were observed, including congenital hypothyroidism and peculiar skeletal abnormalities.
Conclusions: In this study, we report uncommon XGS features associated with five novel truncating variants in AHDC, thus expanding the genotype and phenotypic spectrum of this complex condition. We also compared our cases to previously reported cases, discussing the current status of genotype-phenotype correlations in XGS.
Cinelli G, Della Vecchia S, Bergonzini P, Caramaschi E, Spezia E, Parenti C, Madeo SF, Lucaccioni L, Francesca C, Pugliese M, Raviglione F, Colonna C, Calabrese O, Stanghellini I, Marongiu MC, Biagioni E, Ferrari AR, Battini R, Iughetti L. Clinical, Behavioral and Neuroradiological Phenotype in an Italian Cohort of Patients With Xia Gibbs Syndrome: A Multicenter Cross-Sectional Study and Systematic Literature Review. Am J Med Genet A. 2026 Sep;200(9):2067-2079. doi: 10.1002/ajmg.a.70163. Epub 2026 Apr 30. PMID: 42059486.
Abstract
Heterozygous variants in the AHDC1 gene are associated with Xia Gibbs Syndrome (XGS), a genetic disorder with a highly variable phenotype. Cognitive impairment, motor delay, language delay, neonatal hypotonia, and sleep apnea are considered "cardinal" signs of the disease. In a multicenter cross-sectional study, we analyzed the genetic, epileptological, behavioral, and neuroradiological features of 15 patients with XGS harboring heterozygous variants in AHDC1. The phenotype of our patient cohort is almost overlapping with that already reported in the literature. Seizures begin between 2 and 9 years, while EEG is generally characterized by normal background activity with paroxysmal abnormalities in the posterior areas increased by sleep. We systematically analyzed brain imaging findings as the most frequent brain alteration: the thinning of the corpus callosum, followed by posterior fossa malformation and lateral ventricle morphology abnormalities. Regarding psychiatric disorders, we observed neurodevelopmental disorders such as ID, language disorders, Autism spectrum disorders (ASD), and ADHD in preschoolers, followed by a prevalence of externalizing problems during childhood and adolescence. Our study showed that epilepsy and brain anomalies are very common among XGS individuals. MRI changes are nonspecific, but their association with other clinical features of the syndrome can guide early diagnosis. EEG abnormalities are present in all epileptic patients in the temporal-occipital regions with the same characteristics, so we could hypothesize that these abnormalities could represent a recognizable EEG pattern of XGS. Behavioral disorders represent an important problem, and longitudinal evaluations are needed to improve the classification of the psychopathological spectrum in XGS.
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