The initial decrease and then quick recovery of 10-CHO-THF levels in FD larvae occurred in consort with the increased expression of mthfd1L, implying a compensatory effect for the up-regulation of mthfd1L. This speculation is supported by the improvement and worsening of microphthalmia in embryos injected with the mRNA and MO to increase and decrease the expression of mthfd1L, respectively. Here, MTHFD1L is linked to microphthalmia.