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First Major Chinese Cohort: The study reports on 18 molecularly confirmed Chinese individuals (17 with ARID1B variants and 1 with a SMARCB1 variant) from 17 unrelated families in Hong Kong, combining them with 2 previously reported cases to analyze 19 Chinese patients with ARID1B variants.
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Ethnic Differences in Phenotype (ARID1B): Compared to previously published Western/global cohorts, the Chinese ARID1B group demonstrated distinct phenotypic prevalence:
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Lower prevalence of: Early feeding problems, autistic features, agenesis/hypoplasia of the corpus callosum (brain malformations), and sparse hair.
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Higher prevalence of: Digital (finger/toe) hypoplasia.
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Age-Dependent Digital Changes: Digital hypoplasia (underdeveloped pinky fingers/toes or nails) was observed to become less noticeable over time as children grew, highlighting an age-dependent evolution of physical traits.
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First Confirmed Maternal Somatic Mosaicism: The study documented the first reported family with maternal somatic mosaicism for an ARID1B variant, which resulted in recurring CSS in multiple offspring. This provides critical clinical evidence that parental mosaicism can lead to recurrence risks in future pregnancies.
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Core Takeaway: This research emphasizes how ethnicity and age influence the presentation of ARID1B-related Coffin–Siris syndrome, while underscoring parental mosaicism testing in family planning.
