MUTATION OF A TYPE-II KERATIN GENE (K6A) IN PACHYONYCHIA-CONGENITA

Pachyonychia congenita (PC) is a rare autosomal dominant condition characterized by multiple ectodermal abnormalities1–3. Patients with Jadassohn-Lewandowsky Syndrome (MIM ♯167200; PC-1) have nail defects (onchyogryposis), palmoplantar hyperkeratosis, follicular hyperkeratosis and oral leukokeratosis4. Those with the rarer Jackson-Lawler Syndrome (MIM ♯167210; PC-2) lack oral involvement but have natal teeth and cutaneous cysts5. Ultra-structural studies have identified abnormal keratin tonofilaments6 and linkage to the keratin gene cluster on chromosome 17 has been found in PC families7. Keratins are the major structural proteins of the epidermis and associated appendages and the nail, hair follicle, palm, sole and tongue are the main sites of constitutive K6, K16 and K17 expression8–10. Furthermore, mutations in K16 and K17 have recently been identified in some PC patients11. Although we did not detect K16 or K17 mutations in PC families from Slovenia, we have found a heterozygous deletion in a K6 isoform (K6a) in the affected members of one family. This 3 bp deletion (AAC) in exon 1 of K6a removes a highly conserved asparagine residue (ΔN170) from position 8 of the 1A helical domain (ΔN8). This is the first K6a mutation to be described and this heterozygous K6a deletion is sufficient to explain the pathology observed in this PC-1 family. © 1995 Nature Publishing Group.