Woolly hair (ORPHA:170)
A rare congenital skin disease defined as an abnormality of the structure of the scalp hair and characterized by extreme kinkiness of the hair.
Epidemiology
Prevalence of woolly hair is unknown.
Clinical description
Woolly hair can either be present at birth or appear in the first months of life. The curls, with an average diameter of 0.5 cm, lie closely together and usually make the hair difficult to comb; in addition, the hair may be more fragile than usual. The hair growth rate is usually normal but the anagen phase may be truncated, with the result that the hair does not grow to be long. Woolly hair either shows a generalized distribution affecting the entire scalp or a localized circumscribed distribution in the form of a woolly hair nevus. A diffuse partial form, manifesting during adolescence and adulthood, have also been described. In many cases, woolly hair is associated with hypotrichosis. Whilst wooly hair may occur as an isolated finding, it is important to exclude manifestations that occur in syndromic forms such as dilated cardiomyopathy and palmoplantar keratoderma (Carvajal syndrome), arrhythmogenic right ventricular cardiomyopathy and palmoplantar keratoderma (Naxos disease), or with growth failure and neurological symptoms (Menkes disease).
Etiology
Isolated forms are mostly due to homozygous or sometimes compound heterozygous mutations in the genes lipase H (LIPH, 3q27.2) and lysophosphatidic acid receptor 6 (LPAR6, 13q14.2), that act along a common pathway which plays an important role in the control of hair growth as well as hair texture. In only very few patients, heterozygous mutations have been reported in two keratin genes, namely KRT74 (12q13.13) and KRT71 (12q13.13). Mutations have also been reported in KRT25 (17q21.2 ). Recently, a new gene locus was reported for woolly hair on chromosome 4q35.1-q35.2 with a potential disease gene with one affected family only. The etiology of diffuse partial woolly hair and of sporadically occurring woolly hair nevi is unknown.
Diagnostic methods
A thorough dermatological examination with an evaluation of the entire integument should be performed and may also identify any associated manifestations. The examination of the hair shafts by light and electron microscopy reveals an elliptical cross section, variations in caliber, axis rotation and kinked formation, as well as non-homogeneous keratinization. In some cases trichorrexis nodosa is evident. If necessary, the anagen/catagen ratio can be determined using a trichogram. In cases of diffuse partial woolly hair, an increase in intermediate follicles can be detected histopathologically.
Differential diagnosis
Differential diagnosis includes acquired progressive curling of the hair, allotrichia circumscripta symmetrica, acquired partial kinky hair and drug-induced kinky hair. Syndromes with woolly hair should also be excluded, such as Naxos disease, Carvajal syndrome, Woolly hair-hypotrichosis-everted lower lip-outstanding ears syndrome, woolly-hair-palmoplantar keratoderma syndrome, and skin fragility-woolly hair-palmoplantar keratoderma syndrome.
Genetic counseling
Generalized forms due to KRT74 and KRT71 mutations are autosomal dominant, and forms due to LIPH and LPAR6 mutations are autosomal recessive. Sporadic forms may also occur. Follicular mosaicism is likely, while an autosomal dominant transmission has also been discussed for diffuse partial woolly hair.
Management and treatment
No treatment is currently available. Depending on their size and location, woolly hair nevi can be excised. Harsh physical and chemical cosmetic treatments should be avoided. If the presence of a syndrome is suspected, an extensive internal investigation, with a detailed cardiological diagnostic examination, is necessary.
Prognosis
Woolly hair is most pronounced during childhood; the manifestations often become less severe in adulthood.

                            Last update: 
                            February 2020


                            - Expert reviewer(s): 
                            Pr Regina BETZ  - Pr Ulrike BLUME-PEYTAVI