Mutations in the hairless gene underlie APL in three families of Pakistani origin

Abstract

Background: Atrichia with papular lesions (APL) (OMIM#209500) is a rare autosomal recessively inherited form of irreversible alopecia characterized by papular lesions of keratin-filled cysts on various regions of the body. Males and females are equally affected and present with a distinct pattern of total hair loss on scalp, axilla and body. It begins shortly after birth with the development of hair loss, and patients are normally devoid of eyelashes and eyebrows. Mutations in the hairless (HR) gene have been previously shown to be responsible for APL.

Objective: In this study, we studied the molecular basis of APL in three unrelated families of Pakistani origin.

Method: Molecular analysis of the HR genes was performed on genomic DNA from probands and family members.

Results: DNA sequencing of the HR gene in family A revealed a novel homozygous 2bp deletion in exon 6 leading to a frameshift and a downstream premature termination codon in exon 8 (1782-83delAG). In family B, we identified a novel homozygous deletion of a G nucleotide at the exon 15-intron 15 boundary, termed 3097delG. Family C carries a previously reported missense mutation consisting of an A-to-G transition at nucleotide 276 resulting in the mutation N970S in exon 14.

Conclusion: Two mutations identified in this study are novel mutations in the HR gene and extend the body of evidence implicating the hairless gene family in the pathogenesis of human skin disorders. The one previously reported mutation suggests it may represent a recurrent mutation, or alternatively, an allele that is widely dispersed around the world.

Fig. 1

(A) Clinical appearance of atrichia with papular lesions in an individual of Pakistani origin (family A). The patient is nearly devoid of scalp hair, eyebrows and eyelashes. Note the papules and dermal cysts on face and scalp. (B) Pedigree of family A of Pakistani origin. (C) The mutation was identified as a deletion AG resulting in a frameshift and a premature termination codon.

Fig. 2

(A) Clinical appearance of atrichia with papular lesions in an individual of Pakistani origin (family B). Note the papules and dermal cysts on face and scalp. (B) Pedigree of family B is of Pakistani origin. (C) The mutation identified was a homozygous deletion G at the intron/exon boundary 15, designated 3097delG. (D) For screening of the 3097delG mutation, mismatch allele-specific PCR was performed. The PCR product, 135 bp in size, was subsequently digested with the EcoNI restriction enzyme. Note that only the PCR product from the wild-type allele was digested into two fragments, 103 and 32 bp in size. The 32 bp fragment was not shown. MWM, molecular weight marker.

Fig. 3

Family C is from the Punjab region of Pakistan. (A) Clinical appearance of atrichia with papular lesions in an individual of Pakistani origin (family C). (B) Pedigree of family C. (C) Restriction endonuclease analysis of the hairless gene with the enzyme DdeI. Note the mutation creates a restriction endonuclease site for the enzyme DdeI in exon 14, resulting in a cleavage into products of 145 and 151 bp. The wild-type allele abolishes a restriction site for that enzyme, resulting in a product of 296 bp. The carrier individuals display the 296 bp band together with the superimposed 145 and 151 bp bands, indicative of the heterozygosity for the mutant allele. (D) The mutation was determined to be a A-to-G transition resulting in the conversion of N970 (AAC) to a S970 codon (AGC) in exon 14, designated N970S.

Fig. 4

The spectrum of mutations in the human hairless gene causing atrichia with popular lesions are superimposed on the genomic organization of the human hairless gene. Exons are represented by bars, introns by the horizontal line. Exon 1 contains the 5′ UTR, exon 2 contains the initiation methionine, and exon 19 the 3′ UTR termination codon. The zinc-finger domain is in exon 6 and highlighted in green, the TR-ID domain is in exon 10, 11, 14, 15 and 16 and is highlighted in blue. The Jumonji C domain is in exon 17 and 18 and highlighted in grey. In this setting the mutations in the hairless gene are listed, including the findings in this paper (underlined).