Genome-wide scan and fine-mapping linkage study of androgenetic alopecia reveals a locus on chromosome 3q26

Androgenetic Alopecia: A Review

This study reviewed the current knowledge on the epidemiology, pathophysiology, clinical presentations, diagnosis, treatment, quality-of-life assessment and recent trends in androgenetic alopecia (AGA). Relevant articles on AGA from PubMed, Google Scholar, Medline and Scopus from 1950 to 2024 were obtained and scrutinized.. Key search words included each term like 'androgenetic alopecia', 'androgenic alopecia', 'pattern baldness' and 'pattern hair loss' AND each term like 'epidemiology', 'pathophysiology', 'genetics', 'hormones', 'micronutrient', 'stress and inflammation', 'growth factors', 'clinical features', 'staging', 'cardiovascular associations', 'diagnosis' and 'management' were used in the search. AGA is a non-scarring hair loss that is exemplified by a progressive decline of hair follicles, or non-functional or dead hair follicles in the scalp in a defined pattern. It is the most common hair loss, more common in men but can also present in younger age as premature AGA. Hormones, genetics, micronutrient deficiency, microinflammation and stress have been implicated, while psychosocial distress and cutaneous correlate of cardiovascular diseases have become sources of relentless research. AGA is a patterned hair loss that is more prevalent in Men. It results from the interactions between hormonal, genetic and other factors which determine the extent of hair loss and associated disorders (psychosocial and cardiovascular). As results of more research become available, the extent of AGA, its comorbidities as well as the full spectrum of their manifestations will continue to be sources of health education and more holistic examination by dermatologists and patients.

Association between androgenetic alopecia and periodontitis

AIM

Androgenic alopecia (AGA) is men's most common form of hair loss. It is affected by changes in the expression and activity of 5αR and the metabolism of testosterone and DHT. There is an association between AGA and systemic inflammatory diseases. We hypothesized that there is an association between AGA and periodontal disease, as inflamed gingiva and periodontal fibroblasts have been shown to express more 5αR. Thus, this study aimed to evaluate the relationship between periodontal disease and AGA and the potential effect of aging on this association.

MATERIALS AND METHODS

Out of a cohort of 1088 individuals, 385 white males aged 25-65 with similar socioeconomic levels and without systemic disease were included. Periodontitis was defined using NHANES data. AGA was evaluated using the Norwood-Hamilton scale. The relationship between AGA, periodontal disease severity, and age was assessed.

RESULTS

There was a correlation between age and baldness (r = .421, p < .001). There was a significant correlation between AGA and periodontal disease in younger patients aged 25-34 and 35-44. (p < .042 and p < .036, respectively). There was no significant correlation between AGA and periodontal disease in the 45-54 and 55-65 age groups (p > .05).

CONCLUSION

There may be a relationship between periodontal disease and AGA in the 25-44 age range, suggesting that this association starts at an early age in adulthood.

Early-onset androgenetic alopecia in China: a descriptive study of a large outpatient cohort

Objective

Methods

Results

Conclusions

Mapping of cis-acting expression quantitative trait loci in human scalp hair follicles

BACKGROUND

The association of molecular phenotypes, such as gene transcript levels, with human common genetic variation can help to improve our understanding of interindividual variability of tissue-specific gene regulation and its implications for disease.

METHODS

With the aim to capture the spectrum of biological processes affected by regulatory common genetic variants (minor allele frequency ≥ 1%) in healthy hair follicles (HFs) from scalp tissue, we performed a genome-wide mapping of cis-acting expression quantitative trait loci (eQTLs) in plucked HFs, and applied these eQTLs to help further explain genomic findings for hair-related traits.

RESULTS

We report 374 high-confidence eQTLs found in occipital scalp tissue, whose associated genes (eGenes) showed enrichments for metabolic, mitotic and immune processes, as well as responses to steroid hormones. We were able to replicate 68 of these associations in a smaller, independent dataset, in either frontal and/or occipital scalp tissue. Furthermore, we found three genomic regions overlapping reported genetic loci for hair shape and hair color. We found evidence to confirm the contributions of PADI3 to human variation in hair traits and suggest a novel potential candidate gene within known loci for androgenetic alopecia.

CONCLUSIONS

Our study shows that an array of basic cellular functions relevant for hair growth are genetically regulated within the HF, and can be applied to aid the interpretation of interindividual variability on hair traits, as well as genetic findings for common hair disorders.

Physiology and Medical Treatments for Alopecia

Androgenetic alopecia (AGA) is the most common hair loss disorder in men and women. The characteristic and reproducible balding pattern in AGA negatively affects self-image and the external perceptions of the balding patient. The phenotypical changes are driven by dihydrotestosterone (DHT) and its precursor testosterone. DHT induces follicle miniaturization and hair cycle changes until resulting hairs no longer extrude through the skin surface. AGA is inherited in a polygenetic pattern and is susceptible to epigenetic and environmental factors. Currently, minoxidil, finasteride, and photolaser therapy are the only Food and Drug Administration-approved medical treatments for AGA.

Androgenetic Alopecia: Relationship to Anthropometric Indices, Blood Pressure and Life-Style Habits

Purpose

The association of androgenetic alopecia (AGA) with cardiovascular risk factors including hypertension, smoking and high body mass index (BMI) has been investigated in several studies. However, the results are discrepant. The aim of the present study was to evaluate the association of AGA with anthropometrics, blood pressure and lifestyle habits.

Patients and Methods

In this case-control study, 256 men with AGA and 256 age-matched healthy controls were evaluated. Systolic and diastolic blood pressures, as well as anthropometric indices were measured. Data on lifestyle habits including smoking, hookah use and alcohol consumption were also collected.

Results

Patients with AGA had significantly lower BMI and lower waist to hip ratio as compared to controls (p = 0.012 and p = 0.002, respectively). Other anthropometrics as well as mean systolic and diastolic blood pressures were not significantly different between the two groups. There was no significant difference between patients and controls in terms of lifestyle habits. Patients with severe AGA (Norwood-Hamilton classification type IV-VII) had significantly higher systolic and diastolic blood pressures as compared to those with mild to moderate AGA (Norwood-Hamilton classification type II, III), but the mean age of the former group was also significantly higher (p < 0.001).

Conclusion

In contrast to some previous studies, our findings did not show a significant association between certain cardiovascular risk factors (such as hypertension and smoking) and AGA. Although lower BMI and lower waist to hip ratio were observed in the patient group, these values were within normal limits and therefore not biologically significant.

Genetic variations associated with response to dutasteride in the treatment of male subjects with androgenetic alopecia

Dutasteride, a dual inhibitor of both type I and II 5α-reductases, is used to treat male pattern hair loss (MPHL). However, patient response to dutasteride varies in each individual, the cause of which is yet to be identified. To identify genetic variants associated with response to dutasteride treatment for MPHL, a total of 42 men with moderate MPHL who had been treated with dutasteride for 6 months were genotyped and analysed by quantitative linear regression, case-control association tests, and Fisher’s exact test. The synonymous single nucleotide polymorphism (SNP) rs72623193 in DHRS9 was most significantly associated with response to dutasteride, followed by the non-synonymous SNP rs2241057 in CYP26B1. Additionally, variants in ESR1, SRD5A1, CYP19A1, and RXRG are suggested to be associated with response to dutasteride. Cumulative effect and interaction among these SNPs were presented in both additive and non-additive models.

Female pattern hair loss: A clinical, pathophysiologic, and therapeutic review

Female pattern hair loss (FPHL) is the most common form of alopecia in women. Affected women may experience psychological distress and impaired social functioning. Early diagnosis and initiation of treatment are desirable because treatments are more effective to avoid the progression of hair loss than stimulating regrowth. Typically, a diagnosis of FPHL can be confirmed by review of a patient's medical history and a physical examination alone. Testing a scalp biopsy is diagnostic but usually not required. In women with signs of hyperandrogenism, an investigation for ovarian or adrenal disorders should be performed. Treatment for FPHL is obscured by myths. The aim of FPHL treatment could be two-fold: Reverse or stabilize the process of hair follicle miniaturization. Mild-to-moderate FPHL in women can be treated with oral antiandrogen therapies (cyproterone acetate and spironolactone) and/or topical minoxidil with good results in many cases. If used correctly, available medical treatments arrest the progression of the disease and reverse miniaturization in most patients with mild-to-moderate FPHL. Hair systems and surgery may be considered for selected cases of severe FPHL.

Study of gene expression alteration in male androgenetic alopecia: evidence of predominant molecular signalling pathways

BACKGROUND

Male androgenetic alopecia (AGA) is the most common form of hair loss in men. It is characterized by a distinct pattern of progressive hair loss starting from the frontal area and the vertex of the scalp. Although several genetic risk loci have been identified, relevant genes for AGA remain to be defined.

OBJECTIVES

To identify biomarkers associated with AGA.

METHODS

Molecular biomarkers associated with premature AGA were identified through gene expression analysis using cDNA generated from scalp vertex biopsies of hairless or bald men with premature AGA, and healthy volunteers.

RESULTS

This monocentric study reveals that genes encoding mast cell granule enzymes, inflammatory mediators and immunoglobulin-associated immune mediators were significantly overexpressed in AGA. In contrast, underexpressed genes appear to be associated with the Wnt/β-catenin and bone morphogenic protein/transforming growth factor-β signalling pathways. Although involvement of these pathways in hair follicle regeneration is well described, functional interpretation of the transcriptomic data highlights different events that account for their inhibition. In particular, one of these events depends on the dysregulated expression of proopiomelanocortin, as confirmed by polymerase chain reaction and immunohistochemistry. In addition, lower expression of CYP27B1 in patients with AGA supports the notion that changes in vitamin D metabolism contributes to hair loss.

CONCLUSIONS

This study provides compelling evidence for distinct molecular events contributing to alopecia that may pave the way for new therapeutic approaches.

Androgenetic alopecia as an indicator of metabolic syndrome and cardiovascular risk

Numerous studies have investigated a probable association between androgenetic alopecia (AGA) and cardiovascular disease (CVD) by researching limited and dispersed parameters. We aimed to evaluate both traditional and non-traditional cardiovascular risk factors in male patients with early-onset AGA. This case-control study included 68 participants: 51 male patients with early-onset AGA and 17 healthy male controls. Patients with AGA were classified into three groups according to the Hamilton-Norwood scale and the presence of vertex hair loss. Traditional and non-traditional cardiovascular risk factors were examined in all study subjects. Metabolic syndrome was diagnosed in 25 patients with AGA and in two control subjects (p < 0.05). The carotid intima-media thickness values were found to be significantly higher in patients with vertex pattern AGA than in patients without vertex baldness and controls (p < 0.05). The pulse-wave velocity values were also found to be significantly higher in patients (p < 0.001). A limitation of this study was the small study population. In conclusion, vertex pattern AGA appears to be a marker for early atherosclerosis. This finding supports the hypothesis that early-onset AGA alone could be an independent risk factor for CVD and metabolic syndrome.

Study of the International Epidemiology of Androgenetic Alopecia in Young Caucasian Men Using Photographs From the Internet

BACKGROUND

The epidemiological evaluation of androgenetic alopecia (AGA) is based mainly on direct observation and questionnaires. The international epidemiology and environmental risk factors of AGA in young Caucasian men remain unknown.

AIM

To use photographs and data from the Internet to evaluate severe AGA and generate greater understanding of the international epidemiology of the disorder in young Caucasian men.

MATERIALS AND METHODS

A population-based cross-sectional study design was used. The sample included 26,340 Caucasian men aged 30 to 40 years who had uploaded profiles to two dating websites. Their photographs were evaluated for AGA and graded as follows: severe AGA (Norwood type VI-VII), non-severe AGA, and unknown. Epidemiological data were collected from the sites. Logistic regression was used to analyze the effect of risk factors on the prevalence of severe AGA.

RESULTS

The overall success rate for identifying severe AGA by indirect evaluation of Internet photographs was 94%. The prevalence of severe AGA was 15.33% overall and varied significantly by geographical region. The risk of having severe AGA was increased by 1.092 for every year of age between 30 and 40 years. Severe AGA was more prevalent in subjects with higher body mass index.

CONCLUSIONS

Photographs from the Internet can be used to evaluate severe AGA in epidemiological studies. The prevalence of severe AGA in young Caucasian men increases with age and varies by geographical region. Body mass index is an environmental risk factor for severe AGA.

Minoxidil may suppress androgen receptor-related functions

Although minoxidil has been used for more than two decades to treat androgenetic alopecia (AGA), an androgen-androgen receptor (AR) pathway-dominant disease, its precise mechanism of action remains elusive. We hypothesized that minoxidil may influence the AR or its downstream signaling. These tests revealed that minoxidil suppressed AR-related functions, decreasing AR transcriptional activity in reporter assays, reducing expression of AR targets at the protein level, and suppressing AR-positive LNCaP cell growth. Dissecting the underlying mechanisms, we found that minoxidil interfered with AR-peptide, AR-coregulator, and AR N/C-terminal interactions, as well as AR protein stability. Furthermore, a crystallographic analysis using the AR ligand-binding domain (LBD) revealed direct binding of minoxidil to the AR in a minoxidil-AR-LBD co-crystal model, and surface plasmon resonance assays demonstrated that minoxidil directly bound the AR with a K_d value of 2.6 μM. Minoxidil also suppressed AR-responsive reporter activity and decreased AR protein stability in human hair dermal papilla cells. The current findings provide evidence that minoxidil could be used to treat both cancer and age-related disease, and open a new avenue for applications of minoxidil in treating androgen-AR pathway-related diseases.

Relationship between male pattern baldness and the risk of aggressive prostate cancer: an analysis of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

PURPOSE

Male pattern baldness and prostate cancer appear to share common pathophysiologic mechanisms. However, results from previous studies that assess their relationship have been inconsistent. Therefore, we investigated the association of male pattern baldness at age 45 years with risks of overall and subtypes of prostate cancer in a large, prospective cohort—the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial.

METHODS

We included 39,070 men from the usual care and screening arms of the trial cohort who had no cancer diagnosis (excluding nonmelanoma skin cancer) at the start of follow-up and recalled their hair-loss patterns at age 45 years. Hazard ratios (HRs) and 95% CIs were estimated by using Cox proportional hazards regression models with age as the time metric.

RESULTS

During follow-up (median, 2.78 years), 1,138 incident prostate cancer cases were diagnosed, 571 of which were aggressive (biopsy Gleason score ≥ 7, and/or clinical stage III or greater, and/or fatal). Compared with no baldness, frontal plus moderate vertex baldness at age 45 years was not significantly associated with overall (HR, 1.19; 95% CI, 0.98 to 1.45) or nonaggressive (HR, 0.97; 95% CI, 0.72 to 1.30) prostate cancer risk but was significantly associated with increased risk of aggressive prostate cancer (HR, 1.39; 95% CI, 1.07 to 1.80). Adjustment for covariates did not substantially alter these estimates. Other classes of baldness were not significantly associated with overall or subtypes of prostate cancer.

CONCLUSION

Our analysis indicates that frontal plus moderate vertex baldness at age 45 years is associated with an increased risk of aggressive prostate cancer and supports the possibility of common pathophysiologic mechanisms.

Assessment of the usefulness of dihydrotestosterone in the diagnostics of patients with androgenetic alopecia

Introduction

Androgenetic alopecia (AGA) is the most common form of hair loss. Clinically observed hair loss is due to the continuous miniaturization of affected hair follicles. Genetic factors and androgenic factors especially dihydrotestosterone (DHT), which is a testosterone tissue metabolite, play major roles in the pathogenesis of AGA. However, expert opinions about the usefulness of DHT in the diagnosis of this type of alopecia are divided.

Aim

To evaluate the usefulness of DHT level in patients with androgenetic alopecia compared with the control group.

Material and methods

The study comprised 49 subjects: 19 women and 9 men with androgenetic alopecia. The control group consisted of 17 healthy women and 4 men without hair loss.

Results

Increased serum concentrations of DHT were observed in patients with androgenetic alopecia (17 women, 5 men), but also in the control group. The differences in mean values of DHT were not significant according to the types of alopecia and the control group. Increased serum concentrations of DHT were not correlated with the advance of alopecia.

Conclusions

Dihydrotestosterone is the most influential androgen and seems to play a very important role in the pathogenesis of androgenetic alopecia. Based on the results of our study and others, the most important factors would appear to be the genetically-determined sensitivity of the follicles to DHT and their different reactions to androgen concentration.

A tale of two haplotypes: the EDA2R/AR Intergenic region is the most divergent genomic segment between Africans and East Asians in the human genome

Single nucleotide polymorphisms (SNPs) with large allele frequency differences between human populations are relatively rare. The longest run of SNPs with an allele frequency difference of one between the Yoruba of Nigeria and the Han Chinese is found on the long arm of the X chromosome in the intergenic region separating the EDA2R and AR genes. It has been proposed that the unusual allele frequency distributions of these SNPs are the result of a selective sweep affecting African populations that occurred after the out-of-Africa migration. To investigate the evolutionary history of the EDA2R/AR intergenic region, we characterized the haplotype structure of 52 of its highly differentiated SNPs. Using a publicly available data set of 3,000 X chromosomes from 65 human populations, we found that nearly all human X chromosomes carry one of two modal haplotypes for these 52 SNPs. The predominance of two highly divergent haplotypes at this locus was confirmed by use of a subset of individuals sequenced to high coverage. The first of these haplotypes, the α-haplotype is at high frequencies in most of the African populations surveyed and likely arose before the separation of African populations into distinct genetic entities. The second, the β-haplotype, is frequent or fixed in all non-African populations and likely arose in East Africa before the out-of-Africa migration. We also observed a small group or rare haplotypes with no clear relationship to the α- and β-haplotypes. These haplotypes occur at relatively high frequencies in African hunter-gatherer populations, such as the San and Mbuti Pygmies. Our analysis indicates that these haplotypes are part of a pool of diverse, ancestral haplotypes that have now been almost entirely replaced by the α- and β-haplotypes. We suggest that the rise of the α- and β-haplotypes was the result of the demographic forces that human populations experienced during the formation of modern African populations and the out-of-Africa migration. However, we also present evidence that this region is the target of selection in the form of positive selection on the α- and β-haplotypes and of purifying the selection against α/β recombinants.

"Cold" X5 Hairlaser™ used to treat male androgenic alopecia and hair growth: an uncontrolled pilot study

Background

Various trials have been conducted on the management and treatment of androgenic alopecia (AGA) or male pattern hair loss using a variety of laser and light sources.

Methods

For this feasibility study, the population was composed of males between the ages of 20 and 60 years who have been experiencing active hair loss within the last 12 months and the diagnosis of AGA. They also had a Norwood-Hamilton classification of 3, 3A, 3 V, 4, 4A, or 5 for the hair thinning patterns and skin type I, II, III, or IV on the Fitzpatrick skin type scale. This two-arm randomized, parallel group study design employed stratifying randomization to balance treatment assignment within three investigational centers with at least 2 subjects enrolled in each Fitzpatrick skin type.

Results

A statistically significant positive trend in hair growth was observed from this pilot study, to evaluate the efficacy of the novel cold X5 hairlaser device for treating male androgenic alopecia. From the repeated measures analysis of variance, difference in mean hair counts over time was statistically significant (F = 7.70; p-value < 0.0001). Subsequent, linear regression of mean hair counts at each time point was performed, and post-hoc analysis found an increasing trend of hair growth over time that was statistically significant (p-value < 0.0001) with the estimated slope of 1.406. Increased hair counts from the baseline to the end of the 26-week period were found to be strongly significant (p-value = 0.0003).

Conclusion

Albeit, sham device failure and resultant missing data from the control group, the positive trend hair growth, was observed due to the chronic use of X5hairlaser device. This positive benefit while in full agreement with other low laser hair devices requires intensive further investigation.

Trial registration

NCT02067260

Androgenic alopecia is associated with less dietary soy, lower [corrected] blood vanadium and rs1160312 1 polymorphism in Taiwanese communities

Background

Although the genetic basis of androgenic alopecia has been clearly established, little is known about its non-genetic causes, such as environmental and lifestyle factors.

Objective

This study investigated blood and urine heavy metals concentrations, environmental exposure factors, personal behaviors, dietary intakes and the genotypes of related susceptibility genes in patients with androgenic alopecia (AGA).

Design

Age, AGA level, residence area, work hours, sleep patterns, cigarette usage, alcohol consumption, betel nut usage, hair treatments, eating habits, body heavy metals concentrations and rs1998076, rs913063, rs1160312 and rs201571 SNP genotype data were collected from 354 men. Logistic regression analysis was performed to examine whether any of the factors displayed odds ratios (ORs) indicating association with moderate to severe AGA (≧IV). Subsequently, Hosmer-Lemeshow, Nagelkerke R² and accuracy tests were conducted to help establish an optimal model.

Results

Moderate to severe AGA was associated with the AA genotype of rs1160312 (22.50, 95% CI 3.99–126.83), blood vanadium concentration (0.02, 95% CI 0.01–0.04), and regular consumption of soy bean drinks (0.23, 95% CI 0.06–0.85), after adjustment for age. The results were corroborated by the Hosmer-Lemeshow test (P = 0.73), Nagelkerke R² (0.59), accuracy test (0.816) and area under the curve (AUC; 0.90, 0.847–0.951) analysis.

Conclusions

Blood vanadium and frequent soy bean drink consumption may provide protect effects against AGA. Accordingly, blood vanadium concentrations, the AA genotype of rs1160312 and frequent consumption of soy bean drinks are associated with AGA.

Alterations in sensitivity to estrogen, dihydrotestosterone, and xenogens in B-lymphocytes from children with autism spectrum disorder and their unaffected twins/siblings

It has been postulated that androgen overexposure in a susceptible person leads to excessive brain masculinization and the autism spectrum disorder (ASD) phenotype. In this study, the responses to estradiol (E2), dihydrotestosterone (DHT), and dichlorodiphenyldichloroethylene (DDE) on B-lymphocytes from ASD subjects and controls are compared. B cells were obtained from 11 ASD subjects, their unaffected fraternal twins, and nontwin siblings. Controls were obtained from a different cell bank. Lactate dehydrogenase (LDH) and sodium 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction levels were measured after incubation with different concentrations of E2, DHT, and DDE. XTT/LDH ratio, representative of mitochondria number per cell, was calculated. E2, DHT, and DDE all cause “U”-shaped growth curves, as measured by LDH levels. ASD B cells show less growth depression compared to siblings and controls (P < 0.01). They also have reduced XTT/LDH ratios (P < 0.01) when compared to external controls, whereas siblings had values of XTT/LDH between ASD and external controls. B-lymphocytes from people with ASD exhibit a differential response to E2, DHT, and hormone disruptors in regard to cell growth and mitochondrial upregulation when compared to non-ASD siblings and external controls. Specifically, ASD B-lymphocytes show significantly less growth depression and less mitochondrial upregulation when exposed to these effectors. A mitochondrial deficit in ASD individuals is implied.

Androgenetic alopecia: identification of four genetic risk loci and evidence for the contribution of WNT signaling to its etiology

The pathogenesis of androgenetic alopecia (AGA, male-pattern baldness) is driven by androgens, and genetic predisposition is the major prerequisite. Candidate gene and genome-wide association studies have reported that single-nucleotide polymorphisms (SNPs) at eight different genomic loci are associated with AGA development. However, a significant fraction of the overall heritable risk still awaits identification. Furthermore, the understanding of the pathophysiology of AGA is incomplete, and each newly associated locus may provide novel insights into contributing biological pathways. The aim of this study was to identify unknown AGA risk loci by replicating SNPs at the 12 genomic loci that showed suggestive association (5 × 10(-8)<P<10(-5)) with AGA in a recent meta-analysis. We analyzed a replication set comprising 2,759 cases and 2,661 controls of European descent to confirm the association with AGA at these loci. Combined analysis of the replication and the meta-analysis data identified four genome-wide significant risk loci for AGA on chromosomes 2q35, 3q25.1, 5q33.3, and 12p12.1. The strongest association signal was obtained for rs7349332 (P=3.55 × 10(-15)) on chr2q35, which is located intronically in WNT10A. Expression studies in human hair follicle tissue suggest that WNT10A has a functional role in AGA etiology. Thus, our study provides genetic evidence supporting an involvement of WNT signaling in AGA development.

Pattern hair loss in men: diagnosis and medical treatment

Androgenetic alopecia is a common cause of hair loss in both men and women. The exact pathogenesis of androgenetic alopecia is not well understood. As the name implies, the role of androgens and genetic susceptibility predisposes to pattern hair loss due to gradual conversion of terminal hair into vellus hair. Male and female pattern hair loss are clinically distinct entities but histologically indistinguishable. The role of sex hormones in females is less understood. This article discusses current understanding of the etiopathogenesis of hair loss in men, diagnostic tests available, and its medical management.

Characteristics of androgenetic alopecia in asian

Androgenetic alopecia (AGA), or pattern hair loss, is a common disorder in Asian men and women, with a reported incidence of up to 73% among general population. There are several descriptions regarding the characteristics of AGA in patients of European descent. Asian patients with AGA have different types of hair loss and family histories from Europeans, which may affect treatment response. Therefore, in this review, prevalence, hair loss patterns, familial factors, androgen receptor gene polymorphisms of Asian AGA patients, and management based on algorithmic guidelines for AGA are discussed. This review may be useful for dermatologists in clinical practice for diagnosing and designing management approaches for Asian patients with AGA.

The role of androgen and androgen receptor in skin-related disorders

Androgen and androgen receptor (AR) may play important roles in several skin-related diseases, such as androgenetic alopecia and acne vulgaris. Current treatments for these androgen/AR-involved diseases, which target the synthesis of androgens or prevent its binding to AR, can cause significant adverse side effects. Based on the recent studies using AR knockout mice, it has been suggested that AR and androgens play distinct roles in the skin pathogenesis, and AR seems to be a better target than androgens for the treatment of these skin diseases. Here, we review recent studies of androgen/AR roles in several skin-related disorders, including acne vulgaris, androgenetic alopecia and hirsutism, as well as cutaneous wound healing.

Gender-specific association of androgenetic alopecia with metabolic syndrome in a middle-aged Korean population

BACKGROUND

Although several previous studies have investigated the association between metabolic syndrome (MetS) and androgenetic alopecia (AGA), the study results have been inconsistent.

OBJECTIVES

The aim of this study was to investigate the relationship between the presence of MetS and AGA according to gender in a middle-aged Korean population.

METHODS

A population-based cross-sectional study was conducted on a sample from the Korean Genome Epidemiology Study. In total, 3408 subjects (1707 men and 1701 women) were enrolled between January 2008 and February 2010. The Norwood classification for men and Ludwig classification for women were used for assessment of the degree of hair loss. Information on components of MetS together with other possible risk factors was collected.

RESULTS

In men, the risk of having Norwood type IV or greater was not increased for subjects with MetS compared with those without MetS. In women, the risk of having Ludwig type I or greater was significantly increased for subjects with MetS compared with those without MetS after controlling for age and smoking status (OR 1.68, 95% CI 1.14-2.48; P=0.01). Similar results were also observed for the number of fulfilled components of MetS [odds ratio (OR) 1.38, 95% confidence interval (CI) 1.00-1.91; P<0.05]. When each component of MetS was considered individually, associations between AGA and all five components of MetS (waist circumference, triglycerides, high-density lipoprotein-C, blood glucose, and blood pressure) were not statistically significant. When multiple regression was used to adjust for age, family history and smoking, there was no significant association between the prevalence of MetS and moderate to severe AGA in the male group. On the contrary, a statistically significant positive association was noted between the prevalence of MetS and AGA in the female group.

CONCLUSIONS

Our analysis of AGA and the prevalence of MetS in a large population-based cohort demonstrated quite different findings compared with previous reports. The different results according to gender suggest that there may be different mechanisms that are yet to be defined between male and female AGA.

Susceptibility variants on chromosome 7p21.1 suggest HDAC9 as a new candidate gene for male-pattern baldness

BACKGROUND

Male-pattern baldness (androgenetic alopecia, AGA) is the most common form of hair loss among humans. Research has shown that it is caused by genetic factors. Numerous studies have unequivocally identified two major genetic risk loci for AGA: the X-chromosomal AR/EDA2R locus, and the PAX1/FOXA2 locus on chromosome 20.

OBJECTIVES

To identify further candidate genes for AGA, and thus gain further insights into this phenotype.

METHODS

A German sample of 581 severely affected cases and 617 controls was used to perform a genome-wide association study. The identified associated locus was further analysed by fine-mapping, and then independently replicated in an Australian sample. Expression and pathway analyses were performed to characterize the susceptibility gene identified.

RESULTS

The most significant association signal was obtained for rs756853 (P = 1·64 × 10(-7) ), which is located intronically in the histone deacetylase 9 (HDAC9) gene. Fine-mapping and a family-based analysis revealed that rs756853 and the 6-kb distal rs2249817 were the most highly associated single nucleotide polymorphisms. The association finding was replicated in an independent Australian sample, when the analysis was restricted to severely affected cases and unaffected controls (P = 0·026). Analysis of rs2249817 in a combined sample of severely affected German and Australian cases and unaffected controls revealed a strong association signal (P = 9·09 × 10(-8) ). Tissue expression studies demonstrated HDAC9 expression in various tissues, including tissues of relevance to AGA. No strong genotypic effects were observed in genotype-specific expression or splice studies. Pathway analyses supported the hypothesis that HDAC9 plays a functional role in AGA via interaction with the AR gene.

CONCLUSIONS

The present study suggests that HDAC9 is the third AGA susceptibility gene.

Role of genetics and sex steroid hormones in male androgenetic alopecia and female pattern hair loss: an update of what we now know

The role of genetic predisposition and the influence of sex steroid hormones are indisputable to the pathogenesis of male androgenetic alopecia (MAGA). The role of sex steroid hormones in female pattern hair loss (FPHL) is less known. A good knowledge of the pathophysiology underlying MAGA and FPHL empowers the clinician to confidently counsel patients and make informed therapeutic decisions. Vigorous research in recent years has provided greater insight into the role of genetics and sex steroids in physiological hair growth and cycling, as well as in hair follicle miniaturization, the histological hallmark of MAGA and FPHL. In the present review article directed towards clinicians, we discuss the current understanding of the role of androgens and oestrogens, as well as genetic associations with MAGA and FPHL. We also briefly discuss the interpretation of direct-to-consumer genetic testing for baldness to help clinicians understand the limitations of such tests.

Role of polymorphism of the androgen receptor gene andnon-random x chromosome inactivation in the pathogenesisof androgenic alopecia

The article presents data on molecular and genetic studies of mechanisms of development of androgenic alopecia as well as correlation between polymorphism of the androgen receptor gene by the CAG repeat length in exon 1 and androgen-dependent diseases including alopecia.

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 beta-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.

Genetik der androgenetischen Alopezie

Die androgenetische Alopezie (AGA, erblich- bzw. hormonbedingter Haarausfall [MIM 109200; MIM 300710; MIM 612421]) ist die häufigste Form des Haarverlusts beim Menschen, wobei die Prävalenz stark altersabhängig ist. Im Alter von über 70 Jahren sind über 80% der europäischen Männer betroffen, bei Frauen liegt die AGA-Häufigkeit mit 30–40% deutlich niedriger. Die AGA führt, v. a. bei betroffenen Frauen, zu einer erheblichen psychologischen Belastung und entfaltet dabei Krankheitswert. Der Haarverlust geht auf einen veränderten Haarzyklus und eine Miniaturisierung des Haarfollikels zurück. Die Pathogenese ist androgenabhängig, und die genetische Anlage ist wesentliche Voraussetzung für den Phänotyp. In mehreren Studien konnten der Androgenrezeptor-/Ektodysplasin-A2-Rezeptor(EDA2R)-Locus auf dem X-Chromosom als stärkster beitragender Faktor und durch genomweite Assoziationsuntersuchungen ein weiterer Locus auf Chromosom 20p11 identifiziert werden. Das zum Assoziationssignal nächstgelegene in der Kopfhaut exprimierte Gen ist „paired box 1“ (PAX1). Zwischen PAX1 und dem Androgensignalweg gibt es keine offensichtliche Verbindung, jedoch sind die dem Assoziationssignal auf Chromosom 20p11 zugrunde liegenden pathophysiologischen Prozesse noch nicht geklärt. Bis heute ermöglichen die zur Verfügung stehenden medikamentösen Therapien der AGA bestenfalls ein Aufhalten des Haarverlusts. Mit der Identifizierung der AGA-assoziierten Gene und der Aufklärung ihrer Funktionen wird man die biologischen Ursachen der AGA schrittweise erschließen. Damit ist die Hoffnung auf die Entwicklung neuer Therapien verbunden.

Recent positive selection of a human androgen receptor/ectodysplasin A2 receptor haplotype and its relationship to male pattern baldness

Genetic variants in the human androgen receptor gene (AR) are associated with male pattern baldness (androgenetic alopecia, AGA) in Europeans. Previous observations of long-range linkage disequilibrium at the AR locus are consistent with the hypothesis of recent positive selection. Here, we further investigate this signature and its relationship to the AGA risk haplotype. The haplotype homozygosity suggests that the AGA risk haplotype was driven to high frequency by positive selection in Europeans although a low meiotic recombination rate contributed to the high haplotype homozygosity. Further, we find high levels of population differentiation as measured by F(ST) and a series of fixed derived alleles along an extended region centromeric to AR in the Asian HapMap sample. The predominant AGA risk haplotype also carries the putatively functional variant 57K in the flanking ectodysplasin A2 receptor gene (EDA2R). It is therefore probable that the AGA risk haplotype rose to high frequency in combination with this EDA2R variant, possibly by hitchhiking on a positively selected 57K haplotype.

Androgens and hair loss

PURPOSE OF REVIEW

Androgenetic alopecia (AGA) or male pattern hair loss is a very common condition that has a significant psychosocial impact for patients. Many advances in the pathogenesis and treatment of AGA have been discovered recently. We discuss the pathogenesis and treatment of AGA.

RECENT FINDINGS

Wide genome analysis showed an association of AGA and chromosome 20pll in addition to androgen-receptor gene. Also, a locus on chromosome 3q26 was found to have a linkage with AGA. Dutasteride has been shown to be more effective than finasteride in the treatment of AGA but is not yet a recommended therapy. In an in-vitro study, a new topical liposomal finasteride formulation showed more than five-fold higher deposition of drug in skin than the corresponding plain drug solution.

SUMMARY

These recent developments in the field of AGA hold some promise and may play a role in the future management.

Androgens and hair growth

Hair's importance in human communication means that abnormalities like excess hair in hirsutism or hair loss in alopecia cause psychological distress. Androgens are the main regulator of human hair follicles, changing small vellus follicles producing tiny, virtually invisible hairs into larger intermediate and terminal follicles making bigger, pigmented hairs. The response to androgens varies with the body site as it is specific to the hair follicle itself. Normally around puberty, androgens stimulate axillary and pubic hair in both sexes, plus the beard, etc. in men, while later they may also inhibit scalp hair growth causing androgenetic alopecia. Androgens act within the follicle to alter the mesenchyme-epithelial cell interactions, changing the length of time the hair is growing, the dermal papilla size and dermal papilla cell, keratinocyte and melanocyte activity. Greater understanding of the mechanisms of androgen action in follicles should improve therapies for poorly controlled hair disorders like hirsutism and alopecia.