Answer:
DNA ligase
Explanation:
DNA ligase is an enzyme that responsible for the joining of two DNA strands by the formation of a bond between the deoxyribose group of one DNA strand and the phosphate group of the other DNA strand. DNA ligase is responsible for sealing recombination fragments, connects okazaki fragments formed during DNA replication and also sealing DNA during repairs.
DNA ligase deficiency also referred to as ligas 4 syndrome is characterized by severe growth delays, combined immunodeficiences and abnormal facial structure.
Therefore, in the case of this child with this disease, the enzyme likely to be defective is DNA ligase.