Androgen receptor copy number variation and androgenetic alopecia: a case-control study

Analysis of 72,469 UK Biobank exomes links rare variants to male-pattern hair loss

Male-pattern hair loss (MPHL) is common and highly heritable. While genome-wide association studies (GWAS) have generated insights into the contribution of common variants to MPHL etiology, the relevance of rare variants remains unclear. To determine the contribution of rare variants to MPHL etiology, we perform gene-based and single-variant analyses in exome-sequencing data from 72,469 male UK Biobank participants. While our population-level risk prediction suggests that rare variants make only a minor contribution to general MPHL risk, our rare variant collapsing tests identified a total of five significant gene associations. These findings provide additional evidence for previously implicated genes (EDA2R, WNT10A) and highlight novel risk genes at and beyond GWAS loci (HEPH, CEPT1, EIF3F). Furthermore, MPHL-associated genes are enriched for genes considered causal for monogenic trichoses. Together, our findings broaden the MPHL-associated allelic spectrum and provide insights into MPHL pathobiology and a shared basis with monogenic hair loss disorders.

Male-pattern hair loss: Comprehensive identification of the associated genes as a basis for understanding pathophysiology

Male-pattern hair loss (MPHL) is a highly heritable and prevalent condition that is characterized by progressive hair loss from the frontotemporal and vertex scalp. This androgen-dependent hair loss may commence during puberty, and up to 80 % of European men experience some degree of MPHL during their lifetime. Current treatment options for MPHL have limited efficacy, and improved understanding of the underlying biological causes is required to facilitate novel therapeutic approaches. To date, molecular genetic studies have identified 389 associated genomic regions, have implicated numerous genes in these regions, and suggested pathways that are likely to contribute to key pathophysiological mechanisms in MPHL. This review provides an overview of the current status of MPHL genetic research. We discuss the most significant achievements, current challenges, and anticipated developments in the field, as well as their potential to advance our understanding of hair (loss) biology, and to improve hair loss prediction and treatment.

Hormonal regulation in male androgenetic alopecia-Sex hormones and beyond: Evidence from recent genetic studies

Male-pattern hair loss, also termed androgenetic alopecia (AGA), is a highly prevalent age-related condition that is characterized by a distinct pattern of hair loss from the frontotemporal and vertex regions of the scalp. The phenotype is highly heritable and hormone dependent, with androgens being the recognized critical hormonal factor. Numerous molecular genetic studies have focused on genetic variation in and around the gene that encodes the androgen receptor. More recently, however, the availability of high-throughput molecular genetic methods, novel methods of data analysis and sufficiently large sample sizes have rendered possible the systematic investigation of the contribution of other components of the androgen receptor pathway or hormonal pathways beyond the androgen receptor signalling pathways. Over the past decade, genome-wide association studies of increasingly large cohorts have enabled the genome-wide identification of genetic risk factors for AGA, and yielded unprecedented insights into the underlying pathobiology. The present review discusses some of the most intriguing genetic findings on the relevance of (sex)hormonal signalling in AGA.

Androgenetic alopecia: a review

PURPOSE

Androgenetic alopecia, commonly known as male pattern baldness, is the most common type of progressive hair loss disorder in men. The aim of this paper is to review recent advances in understanding the pathophysiology and molecular mechanism of androgenetic alopecia.

METHODS

Using the PubMed database, we conducted a systematic review of the literature, selecting studies published from 1916 to 2016.

RESULTS

The occurrence and development of androgenetic alopecia depends on the interaction of endocrine factors and genetic predisposition. Androgenetic alopecia is characterized by progressive hair follicular miniaturization, caused by the actions of androgens on the epithelial cells of genetically susceptible hair follicles in androgen-dependent areas. Although the exact pathogenesis of androgenetic alopecia remains to be clarified, research has shown that it is a polygenetic condition. Numerous studies have unequivocally identified two major genetic risk loci for androgenetic alopecia, on the X-chromosome AR⁄EDA2R locus and the chromosome 20p11 locus.

CONCLUSIONS

Candidate gene and genome-wide association studies have reported that single-nucleotide polymorphisms at different genomic loci are associated with androgenetic alopecia development. A number of genes determine the predisposition for androgenetic alopecia in a polygenic fashion. However, further studies are needed before the specific genetic factors of this polygenic condition can be fully explained.

Immunohistochemical evaluation of androgen receptor and nerve structure density in human prepuce from patients with persistent sexual side effects after finasteride use for androgenetic alopecia

Finasteride is an inhibitor of 5-α-reductase used against male androgenetic alopecia (AGA). Reported side effects of finasteride comprise sexual dysfunction including erectile dysfunction, male infertility, and loss of libido. Recently these effects were described as persistent in some subjects. Molecular events inducing persistent adverse sexual symptoms are unexplored. This study was designed as a retrospective case-control study to assess if androgen receptor (AR) and nerve density in foreskin prepuce specimens were associated with persistent sexual side effects including loss of sensitivity in the genital area due to former finasteride use against AGA. Cases were 8 males (aged 29–43 years) reporting sexual side effects including loss of penis sensitivity over 6 months after discontinuation of finasteride who were interviewed and clinically visited. After informed consent they were invited to undergo a small excision of skin from prepuce. Controls were 11 otherwise healthy matched men (aged 23–49 years) who undergone circumcision for phimosis, and who never took finasteride or analogues. Differences in AR expression and nerve density in different portions of dermal prepuce were evaluated in the 2 groups. Density of nuclear AR in stromal and epithelial cells was higher in cases (mean 40.0%, and 80.6% of positive cells, respectively) than controls (mean 23.4%, and 65.0% of positive cells, respectively), P = 0.023 and P = 0.043, respectively. Conversely, percentage of vessel smooth muscle cells positive for AR and density of nerves were similar in the 2 groups. The ratio of AR positive stromal cells % to serum testosterone concentrations was 2-fold higher in cases than in controls (P = 0.001). Our findings revealed that modulation of local AR levels might be implicated in long-term side effects of finasteride use. This provides the first evidence of a molecular objective difference between patients with long-term adverse sexual effects after finasteride use versus drug untreated healthy controls in certain tissues.

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.