TMEM165-CDG has first been reported in 2012 and manganese supplementation was shown highly efficient in rescuing glycosylation in isogenic KO cells. The unreported homozygous missense c.928G>C; p.Ala310Pro variant leading to a functional but unstable protein was identified. This patient was diagnosed at 2 months and displays a predominant bone phenotype and combined defects in N-, O- and GAG glycosylation. We administered for the first time a combined D-Gal and Mn2+ therapy to the patient. This fully suppressed the N-; O- and GAG hypoglycosylation. There was also striking improvement in biochemical parameters and in gastrointestinal symptoms. This study offers exciting therapeutic perspectives for TMEM165-CDG.