Lynn Petukhova

Genome-wide association study in alopecia areata implicates both innate and adaptive immunity

Alopecia areata (AA) is among the most highly prevalent human autoimmune diseases, leading to disfiguring hair loss due to the collapse of immune privilege of the hair follicle and subsequent autoimmune attack. The genetic basis of AA is largely unknown. We undertook a genome-wide association study (GWAS) in a sample of 1,054 cases and 3,278 controls and identified 139 single nucleotide polymorphisms that are significantly associated with AA (P ≤ 5 × 10−7). Here we show an association with genomic regions containing several genes controlling the activation and proliferation of regulatory T cells (Treg cells), cytotoxic T lymphocyte-associated antigen 4 (CTLA4), interleukin (IL)-2/IL-21, IL-2 receptor A (IL-2RA; CD25) and Eos (also known as Ikaros family zinc finger 4; IKZF4), as well as the human leukocyte antigen (HLA) region. We also find association evidence for regions containing genes expressed in the hair follicle itself (PRDX5 and STX17). A region of strong association resides within the ULBP (cytomegalovirus UL16-binding protein) gene cluster on chromosome 6q25.1, encoding activating ligands of the natural killer cell receptor NKG2D that have not previously been implicated in an autoimmune disease. By probing the role of ULBP3 in disease pathogenesis, we also show that its expression in lesional scalp from patients with AA is markedly upregulated in the hair follicle dermal sheath during active disease. This study provides evidence for the involvement of both innate and acquired immunity in the pathogenesis of AA. We have defined the genetic underpinnings of AA, placing it within the context of shared pathways among autoimmune diseases, and implicating a novel disease mechanism, the upregulation of ULBP ligands, in triggering autoimmunity.

Alopecia areata is driven by cytotoxic T lymphocytes and is reversed by JAK inhibition

Alopecia areata (AA) is a common autoimmune disease resulting from damage of the hair follicle by T cells. The immune pathways required for autoreactive T cell activation in AA are not defined limiting clinical development of rational targeted therapies. Genome-wide association studies (GWAS) implicated ligands for the NKG2D receptor (product of the KLRK1 gene) in disease pathogenesis. Here, we show that cytotoxic CD8+NKG2D+ T cells are both necessary and sufficient for the induction of AA in mouse models of disease. Global transcriptional profiling of mouse and human AA skin revealed gene expression signatures indicative of cytotoxic T cell infiltration, an interferon-γ (IFN-γ) response and upregulation of several γ-chain (γc) cytokines known to promote the activation and survival of IFN-γ–producing CD8+NKG2D+ effector T cells. Therapeutically, antibody-mediated blockade of IFN-γ, interleukin-2 (IL-2) or interleukin-15 receptor β (IL-15Rβ) prevented disease development, reducing the accumulation of CD8+NKG2D+ T cells in the skin and the dermal IFN response in a mouse model of AA. Systemically administered pharmacological inhibitors of Janus kinase (JAK) family protein tyrosine kinases, downstream effectors of the IFN-γ and γc cytokine receptors, eliminated the IFN signature and prevented the development of AA, while topical administration promoted hair regrowth and reversed established disease. Notably, three patients treated with oral ruxolitinib, an inhibitor of JAK1 and JAK2, achieved near-complete hair regrowth within 5 months of treatment, suggesting the potential clinical utility of JAK inhibition in human AA.

Disruption of P2RY5, an orphan G protein–coupled receptor, underlies autosomal recessive woolly hair

The genetic determinants of hair texture in humans are largely unknown. Several human syndromes exist in which woolly hair comprises a part of the phenotype; however, simple autosomal recessive inheritance of isolated woolly hair has only rarely been reported. To identify a gene involved in controlling hair texture, we performed genetic linkage analysis in six families of Pakistani origin with autosomal recessive woolly hair (ARWH; OMIM 278150). All six families showed linkage to chromosome 13q14.2–14.3 (Z = 17.97). In all cases, we discovered pathogenic mutations in P2RY5, which encodes a G protein–coupled receptor and is a nested gene residing within intron 17 of the retinoblastoma 1 (RB1) gene. P2RY5 is expressed in both Henles and Huxleys layers of the inner root sheath of the hair follicle. Our findings indicate that disruption of P2RY5 underlies ARWH and, more broadly, uncover a new gene involved in determining hair texture in humans.

APCDD1 is a novel Wnt inhibitor mutated in hereditary hypotrichosis simplex

Hereditary hypotrichosis simplex is a rare autosomal dominant form of hair loss characterized by hair follicle miniaturization. Using genetic linkage analysis, we mapped a new locus for the disease to chromosome 18p11.22, and identified a mutation (Leu9Arg) in the adenomatosis polyposis down-regulated 1 (APCDD1) gene in three families. We show that APCDD1 is a membrane-bound glycoprotein that is abundantly expressed in human hair follicles, and can interact in vitro with WNT3A and LRP5—two essential components of Wnt signalling. Functional studies show that APCDD1 inhibits Wnt signalling in a cell-autonomous manner and functions upstream of β-catenin. Moreover, APCDD1 represses activation of Wnt reporters and target genes, and inhibits the biological effects of Wnt signalling during both the generation of neurons from progenitors in the developing chick nervous system, and axis specification in Xenopus laevis embryos. The mutation Leu9Arg is located in the signal peptide of APCDD1, and perturbs its translational processing from the endoplasmic reticulum to the plasma membrane. APCDD1(L9R) probably functions in a dominant-negative manner to inhibit the stability and membrane localization of the wild-type protein. These findings describe a novel inhibitor of the Wnt signalling pathway with an essential role in human hair growth. As APCDD1 is expressed in a broad repertoire of cell types, our findings indicate that APCDD1 may regulate a diversity of biological processes controlled by Wnt signalling.

Genomewide Scan for Linkage Reveals Evidence of Several Susceptibility Loci for Alopecia Areata

Alopecia areata (AA) is a genetically determined, immune-mediated disorder of the hair follicle that affects 1%-2% of the U.S. population. It is defined by a spectrum of severity that ranges from patchy localized hair loss on the scalp to the complete absence of hair everywhere on the body. In an effort to define the genetic basis of AA, we performed a genomewide search for linkage in 20 families with AA consisting of 102 affected and 118 unaffected individuals from the United States and Israel. Our analysis revealed evidence of at least four susceptibility loci on chromosomes 6, 10, 16 and 18, by use of several different statistical approaches. Fine-mapping analysis with additional families yielded a maximum multipoint LOD score of 3.93 on chromosome 18, a two-point affected sib pair (ASP) LOD score of 3.11 on chromosome 16, several ASP LOD scores >2.00 on chromosome 6q, and a haplotype-based relative risk LOD of 2.00 on chromosome 6p (in the major histocompatibility complex locus). Our findings confirm previous studies of association of the human leukocyte antigen locus with human AA, as well as the C3H-HeJ mouse model for AA. Interestingly, the major loci on chromosomes 16 and 18 coincide with loci for psoriasis reported elsewhere. These results suggest that these regions may harbor gene(s) involved in a number of different skin and hair disorders.

Mutations in the Lipase H Gene Underlie Autosomal Recessive Woolly Hair/Hypotrichosis

Woolly hair (WH) is characterized by the presence of fine and tightly curled hair. WH can appear as a symptom of some systemic diseases, or without associated findings (nonsyndromic WH). Nonsyndromic WH is known to be inherited as either an autosomal-dominant (OMIM 194300) or recessive (ARWH; OMIM 278150) trait. In this study, we identified 11 consanguineous families of Pakistani origin with ARWH, as well as associated features including sparse and hypopigmented hair shafts. We first checked for mutations in the P2RY5 gene, which encodes an orphan G-protein-coupled receptor that we recently identified as a cause of ARWH. However, none of the 11 families had mutations in the P2RY5 gene. To identify the disease locus, we performed linkage studies in one of these families using the Affymetrix 10K array, and identified a region of suggestive linkage on chromosome 3q27. This region contains the lipase H (LIPH) gene which has been recently shown to underlie an autosomal-recessive form of hypotrichosis. Mutation analysis resulted in the identification of a total of 5 pathogenic mutations in the LIPH of all 11 families analyzed. These results show that LIPH is a second causative gene for ARWH/hypotrichosis, giving rise to a phenotype clinically indistinguishable from P2RY5 mutations.

Genome-wide meta-analysis in alopecia areata resolves HLA associations and reveals two new susceptibility loci

Alopecia areata (AA) is a prevalent autoimmune disease with ten known susceptibility loci. Here we perform the first meta-analysis in AA by combining data from two genome-wide association studies (GWAS), and replication with supplemented ImmunoChip data for a total of 3,253 cases and 7,543 controls. The strongest region of association is the MHC, where we fine-map 4 independent effects, all implicating HLA-DR as a key etiologic driver. Outside the MHC, we identify two novel loci that exceed statistical significance, containing ACOXL/BCL2L11(BIM) (2q13); GARP (LRRC32) (11q13.5), as well as a third nominally significant region SH2B3(LNK)/ATXN2 (12q24.12). Candidate susceptibility gene expression analysis in these regions demonstrates expression in relevant immune cells and the hair follicle. We integrate our results with data from seven other autoimmune diseases and provide insight into the alignment of AA within these disorders. Our findings uncover new molecular pathways disrupted in AA, including autophagy/apoptosis, TGFß/Tregs and JAK kinase signaling, and support the causal role of aberrant immune processes in AA.

Autosomal-dominant woolly hair resulting from disruption of keratin 74 (KRT74), a potential determinant of human hair texture.

Autosomal-dominant woolly hair (ADWH) is a rare disorder characterized by tightly curled hair. The molecular basis of ADWH has not previously been reported. In this study, we identified a Pakistani family with ADWH. The family showed linkage to chromosome 12q12-q14.1, containing the type II keratin gene cluster. We discovered a heterozygous mutation, p.Asn148Lys, within the helix initiation motif of the keratin 74 (KRT74) gene in all affected family members. KRT74 encodes the inner root sheath (IRS)-specific epithelial (soft) keratin 74. We demonstrate that the mutant K74 protein results in disruption of keratin intermediate filament formation in cultured cells, most likely in a dominant-negative manner. Furthermore, we sequenced the mouse Krt71-74 genes in the dominant Caracul-like 4 (Cal4) allele, which is characterized by a wavy-coat phenotype and maps to the same region of mouse chromosome 15 as the Caracul (Ca) and Reduced coat (Rco) alleles. We identified a heterozygous mutation, p.Glu440Lys, not in Krt74 but in the neighboring gene, Krt71. Krt71 was previously reported to harbor Ca and Rco mutations, as well as a coding SNP that is associated with curly-coated dogs. In this study, we define the ADWH phenotype resulting from a mutation in a hair-follicle-specific epithelial keratin in humans. Our findings not only further underscore the crucial roles of the IRS-specific epithelial keratin genes Krt71-74 in hair disorders but also open the possibility that these genes might function as genetic determinants of normal variation in hair texture across mammalian species.

Whole-exome sequencing in a single proband reveals a mutation in the CHST8 gene in autosomal recessive peeling skin syndrome.

Generalized peeling skin syndrome (PSS) is an autosomal recessive genodermatosis characterized by lifelong, continuous shedding of the upper epidermis. Using whole-genome homozygozity mapping and whole-exome sequencing, we identified a novel homozygous missense mutation (c.229C>T, R77W) within the CHST8 gene, in a large consanguineous family with non-inflammatory PSS type A. CHST8 encodes a Golgi transmembrane N-acetylgalactosamine-4-O-sulfotransferase (GalNAc4-ST1), which we show by immunofluorescence staining to be expressed throughout normal epidermis. A colorimetric assay for total sulfated glycosaminoglycan (GAG) quantification, comparing human keratinocytes (CCD1106 KERTr) expressing wild type and mutant recombinant GalNAc4-ST1, revealed decreased levels of total sulfated GAGs in cells expressing mutant GalNAc4-ST1, suggesting loss of function. Western blotting revealed lower expression levels of mutant recombinant GalNAc4-ST1 compared to wild type, suggesting that accelerated degradation may result in loss of function, leading to PSS type A. This is the first report describing a mutation as the cause of PSS type A.

FGF5 is a crucial regulator of hair length in humans

Significance Hair length varies dramatically on different body sites and also varies between individuals. Thus, hair length is a quantitative trait, suggesting inherited differences. In this study, we obtained DNA from families segregating excessively long eyelashes consistent with an autosomal recessive trait. We identified mutations in a single gene, fibroblast growth factor 5 (FGF5), which was homozygous in affected family members only. FGF5 has previously been implicated as a regulator of hair lengths in mammals, with mutations resulting in the well-described angora phenotype. However, until now a human counterpart to this phenotype remained elusive. Here, we present, to our knowledge, the first human counterpart of the angora phenotype, showing that FGF5 underlies trichomegaly and is a crucial regulator of hair growth in humans. Mechanisms that regulate the growth of eyelashes have remained obscure. We ascertained two families from Pakistan who presented with familial trichomegaly, or extreme eyelash growth. Using a combination of whole exome sequencing and homozygosity mapping, we identified distinct pathogenic mutations within fibroblast growth factor 5 (FGF5) that underlie the disorder. Subsequent sequencing of this gene in several additional trichomegaly families identified an additional mutation in FGF5. We further demonstrated that hair fibers from forearms of these patients were significantly longer than hairs from control individuals, with an increased proportion in the growth phase, anagen. Using hair follicle organ cultures, we show that FGF5 induces regression of the human hair follicle. We have identified FGF5 as a crucial regulator of hair growth in humans for the first time, to our knowledge, and uncovered a therapeutic target to selectively regulate eyelash growth.