Catalyzes the transfer of CDP-ribitol to the distal N-acetylgalactosamine of the phosphorylated O-mannosyl trisaccharide (N-acetylgalactosamine-beta-3-N-acetylglucosamine-beta-4-(phosphate-6-)mannose), a carbohydrate structure present in alpha-dystroglycan (DAG1) (PubMed:12471058). This constitutes the first step in the formation of the ribitol 5-phosphate tandem repeat which links the phosphorylated O-mannosyl trisaccharide to the ligand binding moiety composed of repeats of 3-xylosyl-alpha-1,3-glucuronic acid-beta-1 (By similarity). Required for normal location of POMGNT1 in Golgi membranes, and for normal POMGNT1 activity (PubMed:19017726). May interact with and reinforce a large complex encompassing the outside and inside of muscle membranes (PubMed:19017726, PubMed:22922256). Could be involved in brain development (Probable). 3-O-[beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-(O-6-P-alpha-D-Man)]-Thr-[protein] + CDP-L-ribitol = 3-O-[Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-(O-6-P-alpha-D-Man)]-Thr-[protein] + CMP + H(+) Protein modification; protein glycosylation. Forms a complex composed of FKTN/fukutin, FKRP and RXYLT1/TMEM5 (By similarity). Interacts (via transmembrane domain) with POMGNT1; the interaction is direct and is required for normal POMGNT1 location in Golgi membranes (By similarity). In retinal tissue, does not localize with the Golgi apparatus. Expressed in the retina, with highest levels found in the inner segments of photoreceptors and the outer plexiform layer (at protein level) (PubMed:29416295). Expressed at lower levels in the inner and outer nuclear layers, the inner plexiform layers, and the ganglion cell layers of the retina (at protein level) (PubMed:29416295). Expressed in the heart, brain, spleen, lung, liver, skeletal muscle, kidney and testis (PubMed:12471058, PubMed:12408965). Wide distribution of expression throughout embryonic development, most predominantly in the central and peripheral nervous systems. High expression in the ventricular zone of proliferating neurons at 13.5 dpc. Broadly expressed in late embryonic and early postnatal cerebellar neurons, including premigratory granule neurons of the external granule cell layer. Expression is maintained in neurons of the internal granule cell layer after migration is complete. Intense expression in Purkinje cells throughout development. A unique pattern of intense expression in irregularly spaced cell bodies that do not appear to correlate with known parasagittal stripes. Expressed in Bergmann glial scaffolds used by granule cells during early posnatal radial migration. Embryonic lethality (PubMed:19017726). However, when human FCMD disease-causing retrotransposon is introduced into the mouse fukutin gene, alpha-dystroglycan/DAG1 is hypoglycosylated in muscles as is seen in FCMD (congenital muscular dystrophy Fukuyama) patients. Transfer of normal fukutin gene into these knockin mice restores glycosylation of alpha-dystroglycan (PubMed:19017726). Conditional knockout in muscle results in near absence of glycosylated dystroglycan within 18 days of gene deletion. 20 week-old knockout mice show clear dystrophic histopathology and defects in glycosylation near the dystroglycan O-mannose phosphate when excision driven by muscle-specific promoters takes place at 8 dpc or 17 dpc. Earlier gene deletion causes more severe phenotypes (PubMed:22922256). Belongs to the LicD transferase family.