Evaluation of an in house genetic testing method for confirmation of Prader - Willi and Angelman syndromes in Sri Lanka

Introduction: Prader-Willi syndrome (PWS, MIM 17620) and Angelman syndrome (AS, MIM 105830) are caused by imprinting defects of chromosome 15q11-13, with loss of maternal gene expression causing AS and paternal gene expression causing PWS. The diagnosis, once established in most cases using a methylation sensitive PCR test, enables appropriate therapeutic interventions and avoids the need for further genetic investigations. Genetic testing for PWS/AS is limited in Sri Lanka (and other low and middle income countries) mainly because parents are unable to pay for testing as these are not funded by the health service. Methods Ninety cases (44 Male and 46 female) with clinical features suspicious of PWS (n= 37) and AS (n=53) referred by a paediatric endocrinologist and a paediatric neurologist were recruited. Clinical information and blood samples were obtained following informed consent. DNA was extracted and methylation sensitive PCR (MS-PCR) was performed following bisulfite modification of DNA using an in house method and a kit. Results were validated using known positive controls. Parent child trio DNA samples were used in cases with confirmed PWS and AS to determine if the disease was due to a deletion or uniparental disomy. The cost of the MS-PCR testing the two modification methods and the microsatellite analysis was determined. Results Among suspected PWS cases 19/37 were positive while 5/53 suspected AS cases were positive. The lower identification rate of AS is probably related to the overlap of clinical features of this condition with other disorders. The kit based modification method was more reliable, less time consuming and cost effective in our laboratory. Conclusions The kit based modification followed by MS-PCR described here enables more affordable genetic testing of suspected PWS/AS cases and this is likely to improve patient care by targeting appropriate therapy for affected cases. Parental genetic counselling is made possible regarding the low recurrence risk, especially where a deletion or uniparental disomy are confirmed. In MS-PCR negative cases with a strong clinical suspicion of AS, UBE3A mutation testing is required. In addition, imprinting centre mutation/ deletion testing may also be needed in strongly clinically suspected, MS-PCR negative PWS and AS cases.