In haplotype analysis, the inheritance of a chromosomal region within a family can be traced with the help of so-called polymorphic DNA markers. Even if the exact location and sequence of the gene causing the disease is unknown within this area, the inheritance of the mutation can be indirectly inferred by knowing the inheritance of the chromosomal area. Similarly, if a gene is known, an unknown mutation can be indirectly detected. This approach is chosen when direct mutation search in the corresponding gene is too costly. Haplotype analysis is a family investigation. Therefore, it is necessary that as many family members as possible participate in addition to the affected person(s) themselves.