Helicases have important roles in
nucleic acid metabolism, and their prominence is marked by the discovery of
genetic disorders arising from disease-causing mutations. Missense mutations can yield unique insight to molecular functions and basis for disease pathology. XPB or XPD missense mutations lead to
Xeroderma pigmentosum, Cockayne's syndrome,
Trichothiodystrophy, or
COFS syndrome, suggesting that DNA repair and transcription defects are responsible for clinical heterogeneity. Complex phenotypes are also observed for
RECQL4 helicase mutations responsible for
Rothmund-Thomson syndrome,
Baller-Gerold syndrome, or RAPADILINO.
Bloom's syndrome causing missense mutations are found in the conserved helicase and RecQ C-terminal domain of BLM that interfere with helicase function. Although rare, patient-derived missense mutations in the
exonuclease or helicase domain of
Werner syndrome protein exist. Characterization of WRN separation-of-function mutants may provide insight to catalytic requirements for suppression of phenotypes associated with the
premature aging disorder. Characterized FANCJ missense mutations associated with
breast cancer or
Fanconi anemia interfere with FANCJ helicase activity required for DNA repair and the replication stress response. For example, a FA patient-derived mutation in the FANCJ
Iron-
Sulfur domain was shown to uncouple its
ATPase and translocase activity from
DNA unwinding. Mutations in DDX11 (ChlR1) are responsible for Warsaw Breakage syndrome, a recently discovered autosomal recessive cohesinopathy. Ongoing and future studies will address clinically relevant helicase mutations and polymorphisms, including those that interfere with key
protein interactions or exert dominant negative phenotypes (e.g., certain mutant alleles of Twinkle
mitochondrial DNA helicase). Chemical rescue may be an approach to restore helicase activity in loss-of-function helicase disorders. Genetic and biochemical analyses of disease-causing missense mutations in human helicase disorders have led to new insights to the molecular defects underlying aberrant cellular and clinical phenotypes.