Aim: To investigate whether all substitutions in the first hypervariable region (HVR1) in sudden infant death syndrome (SIDS) can be recovered along the maternal line of the family (inherited), or whether SIDS victims have new substitutions compared to maternal relatives (somatic mutations) that may be related to environmental factors.
Methods: Seventy-one SIDS/mother pairs, including 11 families with SIDS, mother and mother's relatives and/or SIDS siblings, were studied. The HVR1 sequence was recorded in the base-pair range 16056-16400. The recorded HVR1 sequence was compared with the Cambridge sequence, and differences were recorded as substitutions. The substitution pattern in the SIDS victims was compared with the pattern found in family members along the maternal line.
Results: All the substitutions found in SIDS victims could be traced in the maternal line of the family; in 5 cases this was observed through three generations, and in 3 cases through four generations.
Discussion: In patients with known mitochondrial (mt) DNA disease, a large number of sequence variants have been found in the D-loop region. Substitutions in the D-loop may be part of a haplotype with mutations elsewhere in the mtDNA.
Conclusion: HVR1 substitutions in SIDS victims are hereditary and not due to somatic mutations.