Abstract: Objective To explore the clinical features of 10 q 22 . 3 q 23 . 3 deletion syndrome combined with hypermethioninemia. Methods The clinical data of 10 q 22 . 3 q 23 . 3 deletion syndrome combined with hypermethioninemia in a child were retrospectively analyzed. Results A male child had special facial features, including prominent forehead, low base of the nose, ocular hypertelorism, epicanthus, slightly upturned apex nasi, moderately philtrum and low ear position, and no other special abnormalities were observed. The detection by tandem mass spectrometry found that methionine (MET) was 306. 02 μmol/L at 72 hours after birth, and rose to 695. 37 μmol/L at recall for examination. Familial verification analysis showed that the father of the child had 10q22.3q23.2 microdeletion syndrome, and the deletion CNV was de novo. The mother of the child carried a heterozygous variation of c. 74 _ 75 delTG (p.Val25GlyfsX7) in MAT1A gene. The final diagnosis genotype of the prohand was 10q22.3q23.2 deletion/c.74_75delTG (p.Val 25 GlyfsX 7 ), which leaded to 10 q 22 . 3 q 23 . 3 microdeletion syndrome with hypermethioninemia. After diagnosis, the proband was given low-methionine diet combined with rehabilitation training. The compliance of the families was so poor that the proband’s MET was controlled at around 700 μmol/L. There was no abnormality in liver function and large motor development. However, the language development was delayed. Conclusions The first case of 10 q 22 . 3 q 23 . 3 microdeletion syndrome combined with hypermethioninemia is reported. The prognosis of 10 q 22 . 3 q 23 . 3 microdeletion syndrome varies greatly because of the incomplete penetrance. When MET exceeds 600 μmol/L, low methionine diet is needed as soon as possible.

Key words: 10 q 22 . 3 -q 23 . 2 deletion syndrome; hypermethioninemia; tandem mass spectrometry; methionine