Retraso global del desarrollo y microcefalia posnatal: síndrome de Bainbridge-Ropers con una nueva variante de novo en ASXL3

Expanding the phenotype of ASXL3-related syndrome: A comprehensive description of 45 unpublished individuals with inherited and de novo pathogenic variants in ASXL3

The study aimed at widening the clinical and genetic spectrum of ASXL3-related syndrome, a neurodevelopmental disorder, caused by truncating variants in the ASXL3 gene. In this international collaborative study, we have undertaken a detailed clinical and molecular analysis of 45 previously unpublished individuals with ASXL3-related syndrome, as well as a review of all previously published individuals. We have reviewed the rather limited functional characterization of pathogenic variants in ASXL3 and discuss current understanding of the consequences of the different ASXL3 variants. In this comprehensive analysis of ASXL3-related syndrome, we define its natural history and clinical evolution occurring with age. We report familial ASXL3 pathogenic variants, characterize the phenotype in mildly affected individuals and discuss nonpenetrance. We also discuss the role of missense variants in ASXL3. We delineate a variable but consistent phenotype. The most characteristic features are neurodevelopmental delay with consistently limited speech, significant neuro-behavioral issues, hypotonia, and feeding difficulties. Distinctive features include downslanting palpebral fissures, hypertelorism, tubular nose with a prominent nasal bridge, and low-hanging columella. The presented data will inform clinical management of individuals with ASXL3-related syndrome and improve interpretation of new ASXL3 sequence variants.

Mosaicism in ASXL3-related syndrome: Description of five patients from three families

De novo pathogenic variants in the additional sex combs-like 3 (ASXL3) gene cause a rare multi-systemic neurodevelopmental disorder. There is growing evidence that germline and somatic mosaicism are more common and play a greater role in genetic disorders than previously acknowledged. There is one previous report of ASXL3-related syndrome caused by de novo pathogenic variants in two siblings suggesting gonadal mosaicism. In this report, we present five patients with ASXL3-related syndrome, describing two families comprising two non-twin siblings harbouring apparent de novo pathogenic variants in ASXL3. Parents were clinically unaffected and there was no evidence of mosaicism from genomic DNA on exome-trio data, suggesting germline mosaicism in one of the parents. We also describe clinical details of a patient with typical features of ASXL3-related syndrome and mosaic de novo pathogenic variant in ASXL3 in 30-35% of both blood and saliva sample on trio-exome sequencing. We expand the known genetic basis of ASXL3-related syndromes and discuss mosaicism as a disease mechanism in five patients from three unrelated families. The findings of this report highlight the importance of taking gonadal mosaicism into consideration when counselling families regarding recurrence risk. We also discuss postzygotic mosaicism as a cause of fully penetrant ASXL3-related syndrome.

Phenotypic characterization of an older adult male with late-onset epilepsy and a novel mutation in ASXL3 shows overlap with the associated Bainbridge-Ropers syndrome

The additional sex combs like 3 gene is considered to be causative for the rare Bainbridge-Ropers syndrome (BRPS), which is characterized by severe intellectual disability, neonatal hypotonia, nearly absent development of speech and language as well as several facial dysmorphisms. Apart from disruptive autistiform behaviors, sleep disturbances and epileptic phenomena may be present. Here, a 47-year-old severely intellectually disabled male is described in whom exome sequencing disclosed a novel heterozygous frameshift mutation in the ASXL3 gene leading to a premature stopcodon in the last part of the last exon. Mutations in this very end 3' of the gene have not been reported before in BRPS. The phenotypical presentation of the patient including partially therapy-resistant epilepsy starting in later adulthood shows overlap with BRPS, and it was therefore concluded that the phenotype is likely explained by the identified mutation in ASXL3.