Woolly hair is a rare congenital abnormality related to the structure of scalp hair, which is characterized by tightly curled, thick, and fragile hair. It can occur as an isolated anomaly or in association with Carvajal syndrome or Naxos disease.

Woolly hair is an inherited disorder; it shows an autosomal dominant or autosomal recessive pattern. In the autosomal dominant variation (ADWH), patients exhibit strong and inconstant degree of tight curling hair throughout the scalp at birth or in the few months of life, but it has no effect on the pigmentation of the hair. Manifestations of ADWH are also noted to become significantly less severe in adulthood.

ADWH is associated with mutations in the KRT74 gene. KRT74 gene plays an important role in hair formation and encodes Cytokeratin-74, which is expressed in the inner root sheath of hair follicles.

Three mutations have been reported in KRT74 gene related to Woolly hair disease. The Splice acceptor site mutation in intron 8 of the KRT74 gene; resulting in truncated or absent of KRT74, the C444G transversion mutation in exon 1, resulting in an Asn148Lys substitution at a highly conserved residue at position 9 within the helix initiation motif, and the G1444A transition in exon 9, resulting in an asp482-to-asn (D482N) substitution.