A genetic study of a rare autoimmune disease identified 20 affected individuals from 10 unrelated families. The disease shows autosomal recessive inheritance pattern, but no mutation has been found in the known genes responsible for the disease. Whole genome sequencing was conducted in 5 affected individuals and 10 unaffected individuals from the same population. A bioinformatics analysis showed a novel variant in a gene on chromosome 6 to be present in all affected individuals but not in unaffected individuals. The variant is predicted to be deleterious and affect the function of the encoded protein. The genetic linkage analysis for the variant showed a LOD score of 3.1. 

What is the most appropriate next step for this genetic analysis?