B4GALNT1 and male infertility: The main features of the male infertility in B4galnt1 KO mice were as follows: (a) disappearance of sperms in the smear of testis (Fig. 2A–D); (b) extremely low serum levels of testosterone (KO: 21.0 ± 4.10 ng·dL−1 vs WT: 386.63 ± 111.90 ng·dL−1); (c) no spermatozoa and polynuclear giant cells in the seminiferous tubules (Fig. 2E–J); (d) accumulation of testosterone in the interstitial Leydig cells (Fig. 4); and (e) lowered excretion of intratesticularly injected testosterone and its restoration by co‐injection with complex gangliosides (Fig. 5).