OBJECTIVE@#To investigate the genetic
etiology,
clinical diagnosis and
treatment of a
child with
pancytopenia,
failure to thrive and pulmonary
infection.@*
METHODS@#Peripheral
blood samples of the
child and her
parents were collected. Genomic
DNA was extracted. Genetic variants associated with
hematological diseases were detected by
high-throughput sequencing.@*RESULTS@#Three variants of TCN2
gene were found, one of which located in
exon 5
upstream(c.581-8A>T), the
parents has carried this variant; one in
exon 6 (c.924_927del), the variant was originated from the
mother; one in
exon 7 (c.973C>T), the variant has ocurred de novo. The variants pathogenic
analysis combined with clinical manifestation,
pancytopenia, the increase in
methylmalonic acid level and increased
homocysteine, the
child was diagnosed with transcobalaminIIdeficiency. The
patient presented with respiratory
infection, which was confirmed to be
pneumocystosis by
lung radioscopy and pathogenic
high-throughput sequencing of broncho-
alveolar lavage fluid. The
patient presented with
acute respiratory distress syndrome during the
treatment with
intramuscular injection of
vitamin B@*CONCLUSION@#We reported a case of
Chinese child with TCNII
deficiency due to novel
gene variant, and analyzed the
pathogenicity of the three variants. The
treatment of TCNII
deficiency with
cobalamin should be individualized.