Novel Hairless mutations in two kindreds with autosomal recessive papular atrichia

Novel pathogenic variants in HR underlie atrichia with papular lesions in a cohort of 10 families

Atrichia with papular lesions (APL) is a hair abnormality characterized by loss of hair on the scalp and rest of the body. In a few cases, hair loss is accompanied by the appearance of keratotic papules on the body. It is inherited in an autosomal recessive manner. Sequence variants in the HR (hairless) gene are responsible for this hair abnormality. Here, we present nine consanguineous families and one nonconsanguineous family with clinical manifestations of APL. Whole exome followed by Sanger sequencing and/or direct Sanger sequencing was performed to identify pathogenic variants. The study revealed seven novel pathogenic variants c.794del;p.(Pro265Argfs*98), c.2921-2936del;p.(Tyr974Leufs*16), c.2889C>A;p.(Cys963*), c.2689C>T;p.(Gln897*), c.3186_3187dup;p.(Gln1063Profs*43), c.560dup;p.(Tyr188Ilefs*131), c.2203+5G>C, c.2776+5G>A, and the previously reported variant c.1837C>T;p.(Arg613*) in HR in these families. The study not only expands the mutational spectrum in the HR gene but also highlights the unusual phenotypic findings and will facilitate genetic counseling of families with members showing various types of hair loss disorders in the local population.

Zinc and skin biology

Of all tissues, the skin has the third highest abundance of zinc in the body. In the skin, the zinc concentration is higher in the epidermis than in the dermis, owing to a zinc requirement for the active proliferation and differentiation of epidermal keratinocytes. Here we review the dynamics and functions of zinc in the skin as well as skin disorders associated with zinc deficiency, zinc finger domain-containing proteins, and zinc transporters. Among skin disorders associated with zinc deficiency, acrodermatitis enteropathica is a disorder caused by mutations in the ZIP4 transporter and subsequent zinc deficiency. The triad acrodermatitis enteropathica is characterized by alopecia, diarrhea, and skin lesions in acral, periorificial, and anogenital areas. We highlight the underlying mechanism of the development of acrodermatitis because of zinc deficiency by describing our new findings. We also discuss the accumulating evidence on zinc deficiency in alopecia and necrolytic migratory erythema, which is typically associated with glucagonomas.

Characterization of hairless (Hr) and FGF5 genes provides insights into the molecular basis of hair loss in cetaceans

Background

Hair is one of the main distinguishing characteristics of mammals and it has many important biological functions. Cetaceans originated from terrestrial mammals and they have evolved a series of adaptations to aquatic environments, which are of evolutionary significance. However, the molecular mechanisms underlying their aquatic adaptations have not been well explored. This study provided insights into the evolution of hair loss during the transition from land to water by investigating and comparing two essential regulators of hair follicle development and hair follicle cycling, i.e., the Hairless (Hr) and FGF5 genes, in representative cetaceans and their terrestrial relatives.

Results

The full open reading frame sequences of the Hr and FGF5 genes were characterized in seven cetaceans. The sequence characteristics and evolutionary analyses suggested the functional loss of the Hr gene in cetaceans, which supports the loss of hair during their full adaptation to aquatic habitats. By contrast, positive selection for the FGF5 gene was found in cetaceans where a series of positively selected amino acid residues were identified.

Conclusions

This is the first study to investigate the molecular basis of the hair loss in cetaceans. Our investigation of Hr and FGF5, two indispensable regulators of the hair cycle, provide some new insights into the molecular basis of hair loss in cetaceans. The results suggest that positive selection for the FGF5 gene might have promoted the termination of hair growth and early entry into the catagen stage of hair follicle cycling. Consequently, the hair follicle cycle was disrupted and the hair was lost completely due to the loss of the Hr gene function in cetaceans. This suggests that cetaceans have evolved an effective and complex mechanism for hair loss.

The role of vitamin D receptor mutations in the development of alopecia

Hereditary Vitamin D Resistant Rickets (HVDRR) is a rare disease caused by mutations in the vitamin D receptor (VDR). The consequence of defective VDR is the inability to absorb calcium normally in the intestine. This leads to a constellation of metabolic abnormalities including hypocalcemia, secondary hyperparathyroidism and hypophosphatemia that cause the development of rickets at an early age in affected children. An interesting additional abnormality is the presence of alopecia in some children depending on the nature of the VDR mutation. The data indicate that VDR mutations that cause defects in DNA binding, RXR heterodimerization or absence of the VDR cause alopecia while mutations that alter VDR affinity for 1,25(OH)(2)D(3) or disrupt coactivator interactions do not cause alopecia. The cumulative findings indicate that hair follicle cycling is dependent on unliganded actions of the VDR. Further research is ongoing to elucidate the role of the VDR in hair growth and differentiation.

Thyroid hormone action on skin

The skin characteristics associated with thyroid hormone are classic. The name "myxedema" refers to the associated skin condition caused by increased glycosaminoglycan deposition in the skin. Generalized myxedema is still the classic cutaneous sign of hypothyroidism. It is caused by deposition of dermal acid mucopolysaccharides, notably hyaluronic acid. Despite its appearance, the skin does not pit with pressure.

Detection of a novel missense mutations in atrichia with papular lesions

BACKGROUND

Atrichia with papular lesions (APL) is a rare inherited disease characterized by early onset of total hair loss, followed by papular lesions over the extensor areas of the body. Recently, mutations in the human hairless (HR) gene have been implicated in its pathogenesis. The identification of mutations in the HR gene is important for differentiating between APL and alopecia universalis (AU).

OBJECTIVE

We compared the HR genes of patients with presumed AU who showed minimal or no response to treatment with the HR genes of healthy controls.

METHODS

The subjects were 11 patients with presumed AU who had not responded to treatments. Fifty healthy people were included as controls for molecular analysis. To screen for mutations, polymerase chain reaction was performed.

RESULTS

DNA analysis identified a novel heterozygous G-to-A transition at nucleotide position 191 in exon 5. The mutation was not found in the controls, other AU patients, or any unaffected family members except for the patients' mother and maternal grandfather, who were heterozygous HR gene carriers.

CONCLUSION

Our study identifies a novel missense mutation in exon 5 of the HR gene in a Korean APL patient previously diagnosed as AU.

Analysis of hairless corepressor mutants to characterize molecular cooperation with the vitamin D receptor in promoting the mammalian hair cycle

The mammalian hair cycle requires both the vitamin D receptor (VDR) and the hairless (Hr) corepressor, each of which is expressed in the hair follicle. Hr interacts directly with VDR to repress VDR-targeted transcription. Herein, we further map the VDR-interaction domain to regions in the C-terminal half of Hr that contain two LXXLL-like pairs of motifs known to mediate contact of Hr with the RAR-related orphan receptor alpha and with the thyroid hormone receptor, respectively. Site-directed mutagenesis indicates that all four hydrophobic motifs are required for VDR transrepression by Hr. Point mutation of rat Hr at conserved residues corresponding to natural mutants causing alopecia in mice (G985W and a C-terminal deletion DeltaAK) and in humans (P95S, C422Y, E611G, R640Q, C642G, N988S, D1030N, A1040T, V1074M, and V1154D), as well as alteration of residues in the C-terminal Jumonji C domain implicated in histone demethylation activity (C1025G/E1027G and H1143G) revealed that all Hr mutants retained VDR association, and that transrepressor activity was selectively abrogated in C642G, G985W, N988S, D1030N, V1074M, H1143G, and V1154D. Four of these latter Hr mutants (C642G, N988S, D1030N, and V1154D) were found to associate normally with histone deacetylase-3. Finally, we identified three regions of human VDR necessary for association with Hr, namely residues 109-111, 134-201, and 202-303. It is concluded that Hr and VDR interact via multiple protein-protein interfaces, with Hr recruiting histone deacetylases and possibly itself catalyzing histone demethylation to effect chromatin remodeling and repress the transcription of VDR target genes that control the hair cycle.

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

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.

Nonsense mutations in the hairless gene underlie APL in five families of Pakistani origin

BACKGROUND

Atrichia with papular lesions (APL) is a rare autosomal recessive form of inherited alopecia. Affected individuals present with a distinct pattern of total hair loss on the scalp, axilla and body shortly after birth and are essentially devoid of eyelashes and eyebrows. This form of hair loss is irreversible and the histology is consistent with an absence of mature hair follicles. In addition to total atrichia, APL patients also present with papules and follicular cysts filled with cornified material. Mutations in the Hairless (HR) gene have been shown to underlie APL.

OBJECTIVE

Here, we studied five unrelated large Pakistani families with clinical manifestations of APL.

METHODS

Based on previous reports of HR mutations in APL, we performed direct DNA sequencing analysis.

RESULTS

DNA sequencing of the HR gene in APL patients revealed three novel nonsense mutations in five unrelated families. All affected individuals were homozygous for a nonsense mutation due to C-to-T transitions at different positions in the amino acid sequence. Two families carry the mutation Q323X (CAG-TAG) in exon 3, two families harbor the mutation Q502X (CAG-TAG) in exon 6, and one family had a mutation at R940X (CGA-TGA) in exon 14. Haplotype analysis revealed that all affected individuals of both APL1 and APL16 families were homozygous for the same haplotype, and likewise, the mutation in families APL2 and APL19 was on the same haplotype.

CONCLUSIONS

We report three novel nonsense mutations in the HR gene in APL. Two of the newly identified mutations, Q323X and Q502X, were found to be shared between unrelated families and marker analysis confirmed an identical homozygous haplotype for APL1 and APL16, and for APL2 and APL19. These findings suggest that Q323X and Q502X did not arise independently, but instead appear to have been propagated in the population. Collectively, these findings contribute further evidence for the involvement of hairless mutations in papular atrichia.

Alopecia areata in a rhesus monkey (Macaca mulatta)

BACKGROUND

A 14-year-old female rhesus monkey (Macaca mulatta) of Chinese origin has been suffering from alopecia universalis since childhood.

METHODS

Recently, the health status of the animal was recorded comprehensively by detailed clinical examination including hematology and serology supplemented by histological and immunohistochemical investigations of skin biopsies and molecular biological techniques to clarify the causes of the persistent hair loss.

RESULTS AND CONCLUSIONS

The hairless gene (hr) nonsense mutation was ruled out by polymerase chain reaction and by sequencing of the corresponding gene. Histological examinations revealed a prominent chronic lymphocytic perifolliculitis and folliculitis affecting anagen stage hair follicles as well as miniaturized hair follicles. Immunohistochemistry using the antibodies CD3, CD20 and CD4 confirmed the diagnosis of a T-cell-mediated autoimmune disease resembling alopecia areata universalis in humans.

Interactions of the Vitamin D Receptor with the Corepressor Hairless

Atrichia with papular lesions (APL) and hereditary vitamin D-resistant rickets have a similar congenital hair loss disorder caused by mutations in hairless (HR) and vitamin D receptor (VDR) genes, respectively. HR is a VDR corepressor, and it has been hypothesized that VDR.HR suppress gene expression during specific phases of the hair cycle. In this study, we examined the corepressor activity of HR mutants (E583V, C622G, N970S, V1056M, D1012N, V1136D, and Q1176X) previously described as the molecular cause of APL as well as HR variants (P69S, C397Y, A576V, E591G, R620Q, T1022A) due to non-synonymous polymorphisms in the HR gene. We found that the corepressor activities of all but one of the pathogenic HR mutants were completely abolished. HR mutant E583V exhibited normal corepressor activity, suggesting that it may not be pathogenic. In co-immunoprecipitation assays, all of the pathogenic HR mutants bound VDR but exhibited reduced binding to histone deacetylase 1 (HDAC1), suggesting that the impaired corepressor activity is due in part to defective interactions with HDACs. The HR variants exhibited two classes of corepressor activity, those with normal activity (C397Y, E591G, R620Q) and those with partially reduced activity (P69S, A576V, T1022A). All of the variants interacted with VDR and HDAC1 with the exception of P69S, which was degraded. When coexpressed with VDR, all of the HR pathogenic mutants and variants increased the level of VDR protein, demonstrating that this function of HR was not impaired by these mutations. This study of HR mutations provides evidence for the molecular basis of APL.

Identification of mutations in the human hairless gene in two new families with congenital atrichia

Congenital atrichia (AUC) is a form of isolated alopecia with an autosomal recessive mode of inheritance. Patients are born with normal hair but this is shed almost completely during the first weeks or months of life and never regrows. In many families the development of papular lesions is noted as an additional phenotypic feature, which defines a related phenotype designated as atrichia with papular lesions (APL). Using positional cloning strategies and the molecular findings in hairless recessive (hr/hr) mice, an animal model for AUC, mutations in the human hairless gene (HR) have been identified as a cause of AUC and APL. To date, more than 20 different mutations of the HR gene have been reported in AUC and APL including different mutation types scattered over the entire HR gene length. In this report, we describe two families of Saudi Arabian and Jewish Iranian origin comprising a number of individuals with clinical features suggestive of AUC. We therefore hypothesized that affected members may carry mutations in the HR gene. After sequencing the complete coding region of the HR gene in the Saudi Arabian family, we identified a homozygous insertion of a G (c.2661dupG; p.Thr888DfsX38) in exon 12, resulting in a premature stop codon. In a Jewish Iranian patient, we identified a homozygous splice site mutation c.1557-1G > T in intron 4. The latter mutation has been previously reported in a compound heterozygous state. In the present report, we describe the second exonic insertion mutation in the human HR gene and the first mutation in exon 12. Our study emphasizes the importance of sequencing the complete coding sequence and exon/intron junctions in the molecular diagnostics of AUC and APL.

Repression of transcription by TSGA/Jmjd1a, a novel interaction partner of the ETS protein ER71

Testis-specific gene A (TSGA) was originally identified in rat and shown to be expressed within the testes. Here, we have cloned the murine homolog [also known as jumonji domain-containing 1a (Jmjd1a)] and for the first time characterized the TSGA protein and its functions. Although murine TSGA is expressed in testes, its mRNA is also present in many other tissues, including heart, thymus, liver, and skin. Immunostaining revealed that TSGA is a nuclear protein, whose N-terminus contains a putative nuclear localization signal. TSGA displays significant homology to a suspected tumor suppressor and coactivator (5qNCA), to a thyroid hormone receptor interacting protein (TRIP8) and to the corepressor Hairless, pointing at a role of TSGA in transcription regulation. Indeed, TSGA contains several functional transcription repression domains. In addition, TSGA interacts both in vitro and in vivo with ER71 (ETS related 71), a transcription factor that is expressed in the testes of adult mice and during embryogenesis. Specifically, the N-terminus of TSGA and the C-terminus of ER71 are primarily engaged in their complex formation. Furthermore, TSGA impairs the ability of ER71 to activate transcription from the matrix metalloproteinase-1 promoter. Thus, TSGA may modulate the function of ER71 and thereby affect spermatogenesis as well as embryonic development.

Hairless suppresses vitamin D receptor transactivation in human keratinocytes

The vitamin D receptor (VDR) and its ligand 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] are required for normal keratinocyte differentiation. Both the epidermis and the hair follicle are disrupted in VDR-null mice. Hairless (Hr), a presumptive transcription factor with no known ligand, when mutated, disrupts hair follicle cycling similar to the effects of VDR mutations. Hr, like VDR, is found in the nuclei of keratinocytes in both epidermis and hair follicle. To investigate the potential interaction between Hr and VDR on keratinocyte differentiation, we examined the effect of Hr expression on vitamin D-responsive genes in normal human keratinocytes. Inhibition of Hr expression in keratinocytes potentiated the induction of vitamin D-responsive genes, including involucrin, transglutaminase, phospholipase C-gamma1, and 25-hydroxyvitamin D-24-hydroxylase (24-hydroxylase) by 1,25(OH)2D3. Overexpression of Hr in human keratinocytes suppressed the induction of these vitamin D-responsive genes by 1,25(OH)2D3. Coimmunoprecipitation, DNA mobility shift assays, and chromatin immunoprecipitation revealed that Hr binds to VDR in human keratinocytes. Hr binding to the VDR was eliminated by 1,25(OH)2D3, which recruited the coactivator vitamin D receptor-interacting protein 205 (DRIP205) to the VDR/vitamin D response element complex. These data indicate that Hr functions as a corepressor of VDR to block 1,25(OH)2D3 action on keratinocytes.

Atrichia with papular lesions in two Pakistani consanguineous families resulting from mutations in the human hairless gene

Atrichia with papular lesions (APL) is a rare autosomal recessive form of total alopecia, characterized by hair loss soon after birth and the development of papular lesions of keratin-filled cysts over extensive areas of the body. Mutations in the hairless (hr) gene, a putative single zinc finger transcription factor, have been implicated in the pathogenesis of this disorder. In the present study, we describe two novel deletion mutations in exons 2 and 8 of the human hairless gene leading to frameshift and downstream premature termination codons in two consanguineous Pakistani families affected with atrichia.

Novel compound heterozygous nonsense mutations in the hairless gene causing atrichia with papular lesions

BACKGROUND

Atrichia with papular lesions (APL) is a rare autosomal recessive condition resulting from mutations in the hairless (HR) gene.

OBJECTIVE

In the present study, we investigated the molecular basis of APL in a non-consanguineous Korean family.

METHODS

Direct automated DNA sequencing of the HR gene and restriction digestion analysis were used to identify and confirm the mutation in our proband.

RESULTS

Sequencing of the HR gene revealed two novel nonsense mutations in exons 2 and 4 which were subsequently confirmed via enzymatic restriction. No mutations have previously been detected in this population.

CONCLUSION

The growing number of heterozygous mutations in non-consanguineous pedigrees supports the hypothesis that APL is more common than previously expected.

Hair Loss Among Elderly Men: Etiology and Impact on Perceived Age

BACKGROUND

Androgenetic alopecia is the most common type of hair loss in men, but little is known about the etiology of androgenetic alopecia in elderly men and its impact on perceived age. Here we used a population-based twin study of men aged 70+ to assess the magnitude of the genetic component affecting hair loss and to examine the association between baldness and perceived age.

METHODS

In the fourth wave of The Longitudinal Study of Aging Danish Twins we obtained digital photos of the face and photos of the vertex area of 739 elderly male twins, including 148 intact twin pairs. The degree of baldness and perceived age were assessed in each twin by five and nine nurses, respectively. The heritability of balding was estimated using structural-equation analysis, and it was tested whether baldness was associated with estimations of age.

RESULTS

The intrapair correlation of degree of balding was consistently higher for monozygotic than for dizygotic twin pairs regardless of the baldness categorization used, and structural-equation analysis revealed a heritability of 79% (95% confidence interval, 0.40--0.85) for the mean baldness index. The remaining variation could be attributed to non-shared environmental effects. There was only a very weak and statistically nonsignificant association between baldness and overestimation of age.

CONCLUSIONS

The majority of the variation in baldness in elderly men can be explained by genetic factors, and hair quantity has little impact on perceived age in elderly men.

A Novel Nonsense Mutation and Polymorphisms in the Mouse Hairless Gene

A novel autosomal recessive mutation arose spontaneously in a breeding colony of Chinese Kunming mice. The characteristics of these mutant mice include progressive irreversible hair loss soon after birth, rhinocerotic appearance, and shorter life span. Histological evaluation of skin revealed the homogeneous enlargement of utriculi, and the formation of several rows of large cysts. Sequencing the complete cDNA of the hairless gene identified two polymorphisms and a homozygous transition for a G-->A at nucleotide position 3110 (exon 12) leading to the substitution of tryptophan by a nonsense codon, designated W911X. This allele was named rhinocerotic and short-lived, with the symbol hr(rhsl). Addition of hairless gene mutation into the expanding hairless mutation database allows further development of genotype/phenotype correlations towards understanding inherited atrichia.

Genetic hair and nail disorders

Hair and nails are skin appendages that share with other ectodermal tissues a common developmental pathway. Inherited disorders affecting these two structures therefore very often involve other epithelial components and present with multiple anomalies, generating both physical and psychological distress among patients and their families. The present review briefly describes major recent advances in our understanding of hair and nail genodermatoses.

Interaction of hairless and thyroid hormone receptor is not involved in the pathogenesis of atrichia with papular lesions

Atrichia with papular lesions (APL) (MIM 209 500) is a rare autosomal recessive disease characterized by early onset of atrichia, followed by a papular eruption within the first years of life. Recent studies demonstrating linkage to chromosome 8p21 and further mutation detection in the hairless gene (HR) have established the molecular basis of APL. This study describes the case of a 16-year-old female with APL due to a missense mutation, D1012N, in the hr-thyroid hormone receptor interacting domain 2 (TRID2) of the HR. Using functional and biochemical analysis, it was determined that this mutation does not significantly affect hr-thyroid hormone receptor interaction. This result suggests that the TRID2 domain either is dispensable in the hr-TR interaction or is not involved in the pathogenesis of APL.

Atrichia with papular lesions resulting from a novel homozygous missense mutation in the hairless gene

Atrichia with papular lesions (APL) is a rare autosomal recessive disorder resulting in complete and irreversible hair loss shortly after birth. Affected individuals also develop papular lesions of keratin-filled follicular cysts over extensive areas of the body. Mutations in the hairless gene, a putative single zinc-finger transcription factor protein, have been implicated in the pathogenesis of APL. In this report, we describe a novel missense mutation, E583V, in the hairless gene in an Italian family affected with APL. The mutation resides between the LXXLL motif found in TRIPs (thyroid hormone receptor interacting proteins) in exon 5 and the six-cysteine zinc-finger motif in exon 6. The amino acid sequence neighbouring the LXXLL motif and zinc-finger domain is highly conserved in human, monkey, rat, and mouse hairless proteins. Our finding extends the body of evidence that supports the importance of the zinc-finger and LXXLL domains in the function of the hairless protein. Moreover, we continue to find small APL families without consanguinity from around the world.

Morphological approach to hair disorders

The Workshop on the morphological approach to hair disorders brought together a group of clinicians involved in hair biology research. Six speakers spoke on a range of topics that can be grouped broadly into a central theme. It summarizes the evolution of medical research. The section by Tosti and coworkers describes a patient with a new unique syndrome. The section by Ferrando and colleagues provides a framework in which patients with rare hair disorders can be classified. The section by Whiting tries to define the normal anatomy of the hair follicle and both horizontal and vertical sections. It is only when normal anatomy has been absolutely defined that pathological deviations can be recognized. The section by Sinclair and coworkers attempts to estimate the reliability of histological diagnosis so that its true value of pathology can be recognized. The section by Zlotogorski and coworkers shows how accurate clinical and histological definition of disease acts as the cornerstone for gene discovery techniques. Once a causative mutation is found and a gene product identified, then the biological consequences of the altered protein product can be studied and the impact of the abnormal molecular function on hair biology can be understood. It is hoped that improved understanding of hair disease will then lead to useful therapeutic interventions. The final section by Leroy and Van Neste highlights the difficulties of evaluating therapeutic interventions in hair loss disease and proposes a new technique.

Compound heterozygosity for mutations in the hairless gene causes atrichia with papular lesions

BACKGROUND

Congenital atrichias represent a complex and heterogeneous group of genodermatoses, which have been shown in several consanguineous families to result from homozygous mutations in the hairless gene (HR).

OBJECTIVES

To identify the molecular basis of congenital atrichia in a non-consanguineous family.

METHODS

Genetic analysis was carried out in a two-generation family with two children with congenital atrichia and one healthy child.

RESULTS

We established a diagnosis of atrichia with papular lesions based on clinical and histopathological data. We identified a heterozygous 11-bp deletion (189-199del) in the two affected children and their mother. In addition, the two affected children and their father were shown to carry a non sense mutation (Q478X), which has previously been described in a Pakistani family. Haplotype analysis revealed that mutation Q478X occurred independently in the two families.

CONCLUSIONS

We have identified the first case of compound heterozygosity for mutations in HR as well as the first instance of a recurrent mutation in this gene. These data further expand our understanding of the molecular pathomechanisms underlying congenital atrichias.

Atrichia with papular lesions resulting from compound heterozygous mutations in the hairless gene: A lesson for differential diagnosis of alopecia universalis

BACKGROUND

Atrichia with papular lesions (APL) is a rare, autosomal recessive form of total alopecia in which mutations in the hairless (HR) gene have been shown to underlie the phenotype.

OBJECTIVE

We suspect that APL is actually much more common than previously believed. We sought to investigate whether APL might also be found among patients in small families, particularly those giving a history of (1) normal hair at birth, which was shed and never regrew, and (2) "alopecia universalis" that is recalcitrant to any treatment.

METHODS

We identified a small family of German origin in which 2 of 4 siblings were affected and gave this clinical history. Direct sequence analysis of the HR gene in the nuclear family was performed.

RESULTS

Mutation analysis revealed distinct mutations on each allele of the HR gene. This is the first demonstration of compound heterozygous mutations underlying APL.

CONCLUSION

These findings support the hypothesis that APL can exist in small nonconsanguineous families and may be masquerading clinically as alopecia universalis. Accurate discrimination between APL and alopecia universalis should prevent unnecessary treatment of patients affected with APL.

A novel missense mutation affecting the human hairless thyroid receptor interacting domain 2 causes congenital atrichia

Congenital atrichias represent a large and heterogeneous group of inherited hair disorders. In this report, we describe a patient affected with alopecia universalis congenita (MIM 203655). Sequence analysis revealed a G to A transition at cDNA position 3034 of the hairless hr gene present in a homozygous state in the patient and in a heterozygous state in the patient's mother, and absent in the patient's sister. The mutation is predicted to result in the substitution of an asparagine residue for an aspartate amino acid (D1012N) at a position previously shown in the rat to affect hairless binding to thyroid hormone receptor. This study presents the first evidence in humans for the functional importance of the hairless thyroid receptor interacting domain 2.

Evidence for pseudodominant inheritance of atrichia with papular lesions

Atrichia with papular lesions is a rare form of total alopecia, in which mutations in the hairless gene have been shown to underlie the phenotype. In the literature to date, atrichia with papular lesions has generally been reported to be inherited in an autosomal recessive manner. A few rare cases exist, however, in which parent-to-child transmission of atrichia with papular lesions has been documented. In this study, further investigations were carried out into the molecular basis of atrichia with papular lesions in a family with mother-to-son transmission by searching for mutations in the human hairless gene. Specific ally, we wanted to determine whether this case truly represented an example of dominantly inherited atrichia with papular lesions, or whether another mode of inheritance might be responsible for the disorder in this kindred. Pseudodominant inheritance, for example, occurs when an individual with a known recessive disorder has a clinically unaffected partner, but then unexpectedly gives birth to children who are affected with the same recessive disorder as the affected parent, and can easily be distinguished from classical dominant inheritance with molecular diagnosis and haplotype analysis. In the family reported here, we have determined that both the mother and son are, in fact, homozygous for a novel mutation in the hairless gene, R33X. We provide the first evidence for pseudodominant inheritance in atrichia with papular lesions, and at the same time extend our knowledge of pathogenetic mutations in the human hairless gene. Importantly, this information allows revisions in genetic counseling for risk of transmission for individuals in the family, previously impossible in the absence of knowing the genetic basis of atrichia with papular lesions in this unusual kindred.

Clinical and molecular diagnostic criteria of congenital atrichia with papular lesions

Congenital atrichia with papular lesions is a rare, autosomal recessive form of total alopecia and mutations in the hairless (hr) gene have been implicated in this disorder. Published estimates of the prevalence of this disorder remain surprisingly low considering pathogenetic mutations in hr have been found in distinct populations around the world. Therefore, it is likely that congenital atrichia with papular lesions is more common than previously thought and is often mistaken for the putative autoimmune form of alopecia universalis. To clarify this discrepancy, we propose criteria for the clinical diagnosis of congenital atrichia with papular lesions. Among these is the novel report of the consistent observation of hypopigmented whitish streaks on the scalp surface of affected individuals. Additionally, we report the identification of a novel missense mutation in hr from a family of Arab Palestinian origin that exhibits the pathognomonic features of atrichia with papular lesions. Collectively, we anticipate that an increased recognition of this disorder will result in more accurate diagnosis and the sparing of unnecessarily treatment to patients.

The hairless gene in androgenetic alopecia: results of a systematic mutation screening and a family-based association approach

BACKGROUND

Genetic disposition and androgen dependence are important characteristics of the common patterned loss of scalp hair known as androgenetic alopecia (AGA). The genetic factors contributing to AGA are currently unknown. The human hairless gene (HR) has recently been cloned and mutations have been reported in families with autosomal recessive universal congenital alopecia and papular atrichia. The main feature of these disorders is persistent complete absence of hair at or shortly after birth. This suggests that HR is essential and specific for the development of hair.

OBJECTIVES

To test the hypothesis that HR may be involved in AGA.

METHODS

We systematically screened HR for genetic variability by means of single-strand conformation analysis (SSCA) in 46 unrelated men with AGA. To test for an involvement of HR in the development of AGA, seven common variants were genotyped in 61 families with 93 affected offspring. The results were analysed with the transmission/disequilibrium test (TDT).

RESULTS

SSCA showed 15 single nucleotide substitutions: eight missense mutations, four silent mutations and three mutations in exon-flanking intronic sequences. TDT results showed a marginally significant association between AGA and variants 3379-29G/T (P = 0.024) and 2611-68C/T (P = 0.047). These results, however, did not remain significant after applying the conservative Bonferroni correction for multiple testing.

CONCLUSIONS

Our results do not provide evidence for a strong involvement of HR in the development of AGA, although a minor role cannot be fully excluded.

Clinical and molecular diagnostic criteria of congenital atrichia with papular lesions

Congenital atrichia with papular lesions is a rare, autosomal recessive form of total alopecia and mutations in the hairless (hir) gene have been implicated in this disorder. Published estimates of the prevalence of this disorder remain surprisingly low considering pathogenetic mutations in hir have been found in distinct ethnicities around the world. Therefore, it is likely that congenital atrichia with papular lesions is far more common than previously thought and is often mistaken for its phenocopy, the putative autoimmune form of alopecia universalis. To clarify this discrepancy, we propose criteria for the clinical diagnosis of congenital atrichia with papular lesions. Among these is the novel report of the consistent observation of hypopigmented whitish streaks on the scalp surface of affected individuals. Additionally, we report the identification of a novel missense mutation in hir from a family of Arab Palestinian origin that exhibits the pathognomonic features of atrichia with papular lesions. Collectively, we anticipate that an increased recognition of this disorder will result in more accurate diagnosis and the sparing of unnecessarily treatment to patients.

The hairless gene mutated in congenital hair loss disorders encodes a novel nuclear receptor corepressor

The mammalian hairless (hr) gene plays a critical role in the maintenance of hair growth. Although the hr gene has been identified, the biochemical function of its encoded protein (Hr) has remained obscure. Here, we show that Hr functions as a transcriptional corepressor for thyroid hormone receptors (TRs). We find that two independent regions of Hr mediate TR binding and that interaction requires a cluster of hydrophobic residues similar to the binding motifs proposed for nuclear receptor corepressors (N-CoR and SMRT). Similarly, we show that Hr binds to the same region of TR as known corepressors. We show that Hr interacts with histone deacetylases (HDACs) and is localized to matrix-associated deacetylase (MAD) bodies, indicating that the mechanism of Hr-mediated repression is likely through associated HDAC activity. Thus, Hr is a component of the corepressor machinery, and despite its lack of sequence identity with previously described corepressors, its mode of action is remarkably conserved. On the basis of its thyroid hormone-inducible and tissue- and developmental-specific expression, Hr likely defines a new class of nuclear receptor corepressors that serve a more specialized role than ubiquitous corepressors. The discovery that Hr is a corepressor provides a molecular basis for specific hair loss syndromes in both humans and mice.

Atrichia caused by mutations in the vitamin D receptor gene is a phenocopy of generalized atrichia caused by mutations in the hairless gene

Generalized atrichia with papules is a rare disorder characterized by loss of hair shortly after birth and development of cutaneous cysts. Mutations in the hairless gene (HR) cause this phenotype in both mouse and human. Here we present a case of atrichia with papules in a patient with a normal HAIRLESS gene but with mutations in both alleles of the VITAMIN D RECEPTOR. The patient exhibited vitamin D resistant rickets, which was confirmed by an absent response of her fibroblasts to 1,25-dihydroxyvitamin D3 in vitro. Similar to individuals with HAIRLESS mutations, her skin showed an absence of normal hair follicles and the presence of follicular remnants and cysts. The cyst epithelium contained keratin-15- and keratin-17-positive cells suggesting derivation from the hair follicle bulge and the presence of epithelial stem cells. Although hair loss has been reported in association with hereditary vitamin D resistant rickets, we now characterize this alopecia as clinically and pathologically indistinguishable from generalized atrichia with papules, which was previously thought to be caused only by mutations in HAIRLESS. These findings suggest that VDR and HR, which are both zinc finger proteins, may be in the same genetic pathway that controls postnatal cycling of the hair follicle.

Topical triiodothyronine stimulates epidermal proliferation, dermal thickening, and hair growth in mice and rats

The skin is a classic target tissue for thyroid hormone action. Although the histology of skin in hypothyroid states is well documented, the literature contains little assessment of skin in thyrotoxic states. In light of the paucity of information on skin under the influence of excess thyroid hormone, we investigated the direct effect of thyroid hormone on skin. Triiodothyronine (T3) was applied topically daily in liposomes to SKH-1 hairless mice for 7 days and to CD rats for 2 weeks. There was a dose-dependent increase in epidermal proliferation, dermal thickening, and hair growth in T3-treated animals. Mice that received 3.8 microg of T3 had 42% more hairs per millimeter than controls (p < 0.01), hair length that was 1,180% longer (p < 0.001), 49% greater epidermal 3H-thymidine incorporation (p < 0.01), and 80% more 5-bromo-2'-deoxyuridine (BrdU) stained cells (p < 0.05). Rats receiving 12.8 microg T3 had 48% greater dermal thickness than controls (p < 0.001), 26% greater epidermal thickness (p < 0.001), 85% more hairs per millimeter (p < 0.005), and 130% greater 3H-thymidine incorporation into the epidermis (p < 0.01). Thus, topically applied thyroid hormone has dramatic effects on both skin and hair growth. These observations offer a new strategy for developing thyroid hormone and its analogues for treating disorders of skin and hair growth.

Recent advances in the molecular basis of inherited skin diseases

Over the last few years the molecular basis of several inherited skin diseases has been delineated. Some discoveries have stemmed from a candidate gene approach using clinical, biochemical, immunohistochemical, and ultrastructural clues, while others have arisen from genetic linkage and positional cloning analyses. Notable advances have included elucidation of specific gene pathology in the major forms of inherited skin fragility, ichthyosis, and keratoderma. These findings have led to a better understanding of the significance of individual structural proteins and regulatory enzymes in keratinocyte adhesion and differentiation. From a clinical perspective, the advances have led to better genetic counseling in many disorders, the development of DNA-based prenatal diagnosis, and a foundation for planning newer forms of treatment, including somatic gene therapy, in selected conditions.

Alopecia areata universalis in an infant

BACKGROUND

Alopecia areata (AA) is common during childhood and rarely reported in infants. The four reported cases of AA in infants all exhibited circumscribed patches of alopecia that appeared at birth or shortly thereafter.

OBJECTIVE

We report a case of alopecia areata universalis that developed after birth along with fingernail changes of shortening (onychomadesis) and onycholysis. Scalp biopsy at 2 years of age revealed rare, intermediate, terminal follicles in catagen associated with sparse peribulbar lymphocytic infiltrates.

RESULTS

This constellation of clinicopathologic features was interpreted as AA. We discuss the differential diagnosis of generalized alopecia in healthy infants, in particular, Clouston's syndrome, a hair-nail (hidrotic) ectodermal dysplasia found in this region. Genetic testing for linked polymorphisms to the Clouston gene locus were negative in this child and his parents.

CONCLUSIONS

Alopecia areata should be included in the differential diagnosis of generalized alopecia presenting at or shortly after birth. For purposes of genetic counseling and prognosis, it is crucial that a correct diagnosis be made.

Alopecia Areata Universalis in an Infant

Background:

Alopecia areata (AA) is common during childhood and rarely reported in infants. The four reported cases of AA in infants all exhibited circumscribed patches of alopecia that appeared at birth or shortly thereafter.

Objective:

We report a case of alopecia areata universalis that developed after birth along with fingernail changes of shortening (onychomadesis) and onycholysis. Scalp biopsy at 2 years of age revealed rare, intermediate, terminal follicles in catagen associated with sparse peribulbar lymphocytic infiltrates.

Results:

This constellation of clinicopathologic features was interpreted as AA. We discuss the differential diagnosis of generalized alopecia in healthy infants, in particular, Clouston's syndrome, a hair-nail (hidrotic) ectodermal dysplasia found in this region. Genetic testing for linked polymorphisms to the Clouston gene locus were negative in this child and his parents.

Conclusions:

Alopecia areata should be included in the differential diagnosis of generalized alopecia presenting at or shortly after birth. For purposes of genetic counseling and prognosis, it is crucial that a correct diagnosis be made.

Hairless is translocated to the nucleus via a novel bipartite nuclear localization signal and is associated with the nuclear matrix

Hair follicle cycling is an exquisitely regulated and dynamic process consisting of phases of growth, regression and quiescence. The transitions between the phases are governed by a growing number of regulatory proteins, including transcription factors. The hairless (hr) gene encodes a putative transcription factor that is highly expressed in the skin, where it appears to be an essential regulator during the regression of the catagen hair follicle. In hairless mice, as well as humans with congenital atrichia, the absence of hr gene function initiates a premature and abnormal catagen due to a dysregulation of apoptosis and cell adhesion, and defects in the signaling required for hair follicle remodeling. Here, we report structure-function studies of the hairless gene product, in which we identify a novel bipartite nuclear localization signal (NLS) of the form KRA(X13) PKR. Deletion analysis of the mouse hr gene mapped the NLS to amino acid residues 409–427. Indirect immunofluorescence microscopy of cells transiently transfected with hairless-green fluorescent fusion proteins demonstrated that these amino acid residues are necessary and sufficient for nuclear localization. Furthermore, nuclear fractionation analysis revealed that the hr protein is associated with components of the nuclear matrix.