METHODOLOGY: Retrospective review of all children who fulfilled the diagnostic criteria of CVS and who were seen at Department of Paediatrics, University of Malaya Medical Centre, Kuala Lumpur and Paediatric Unit, Penang Hospital, Penang, Malaysia from 1987 to 1997.

RESULTS: Eight children with CVS were seen at the two units during the study period, five girls and three boys. All had cyclical, self-limited episodes of nausea and vomiting with symptom-free intervals. The mean age of onset was 5.9 years. The clinical features were similar to other series described in the literature. Only two of the eight children were described as 'perfectionist'. Two children identified stress as precipitating factors. Therapy to reduce the number of emeses during acute attacks and to prevent subsequent attacks had been ineffective.

RESULTS: Twenty-two patients (from 16 unrelated families) were molecularly diagnosed as XLA. Genetic testing revealed fifteen distinct mutations, including four splicing mutations, four missense mutations, three nonsense mutations, three short deletions, and one large indel mutation. These mutations scattered throughout the BTK gene and mostly affected the kinase domain. All mutations including five novel mutations were predicted to be pathogenic or deleterious by in silico prediction tools. Genetic testing confirmed that eleven mothers and seven sisters were carriers for the disease, while three mutations were de novo. Flow cytometric analysis showed that thirteen patients had minimal BTK expression (0-15%) while eight patients had reduced BTK expression (16-64%). One patient was not tested for monocyte BTK expression due to insufficient sample. Pneumonia (n=13) was the most common manifestation, while Pseudomonas aeruginosa was the most frequently isolated pathogen from the patients (n=4). Mild or asymptomatic COVID-19 was reported in four patients.