Думаю, что у вас в тексте опечатка, даже целых две. Вместо cbi и Cdl оба раза должно быть cbl.

cbl = cobalamine = vitamin B12

Five other forms of homocystinuria also reflect impaired conversion of homocysteine to methionine. The primary defects in these entities, however, are in the synthesis of methylcobalamin, a cobalamin (vitamin B12) coenzyme required by methyltetrahydrofolate:homocysteine methyltransferase (see Fig. 349.2). In some, methylmalonic acid accumulates in body fluids because of impaired synthesis of a second coenzyme, adenosylcobalamin, required for isomerization of methylmalonyl coenzyme A (CoA) to succinyl CoA. These disorders are designated cblC, -D, -E, -F, and -G.
As with 5,10-methylenetetrahydrofolate reductase deficiency, each disorder impairs remethylation of homocysteine. Since methylcobalamin is required for methyl-group transfer from methyltetrahydrofolate to homocysteine, impaired cobalamin metabolism leads to deficient methyltransferase activity. The defects responsible for impaired synthesis of methylcobalamin involve one of several steps in lysosomal or cytosolic activation of the vitamin precursor (see Fig. 349.2). In the cblF disorder, the transport of cobalamins out of lysosomes is impaired. In cblC and -D, a reductase needed for formation of both methylcobalamin and adenosylcobalamin is deficient. In cblE and -G, some component required to maintain a reduced form of cobalamin on the methyltransferase apoenzyme is impaired. Somatic cell genetic studies indicate that each of these abnormalities is distinct and imply that all are inherited as autosomal recessive traits.

cbl C, cbl D, cbl E, cbl F и cbl G --
так обозначают типы заболевания, которое называется гомоцистинурия.
Вот здесь можно посмотреть подробно: http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?236200

А methyl Cdl -- это метилкобаламин.