2.4 Sample preparation
The heel blood of the neonatal subjects was collected into a special filter paper, dry naturally at room temperature to form dried blood spots (DBS). After conventional NBS, the DBS was stored at 4 ℃. Genomic DNA was extracted from DBS using QIAamp DNA Mini Kit (Qiagen, German) according to the operation manual. Briefly, a punched-out circle from a DBS was placed into a 1.5 ml microtube with Buffer ATL to dissolve DNA and incubated at 85°C for 10 min. Protein K was added to digest proteins. After 70°C-incubation and adding ethanol, the buffer was transferred into a Mini spin column. Finally, the DNA solution was eluted with Elution buffer after a series of centrifugation. The quality and quantity of the DNA were assessed by Qubit® 3.0 Fluorometer (Thermo Fisher Scientific Inc., USA) according to the instruction.