The HairDX (RxR) Genetic Test
(Finasteride Response and Benign Prostatic Hyperplasia)
Recent advances in human genetics empower researchers to discover the genetic basis of drug response to many common conditions. As genetic science is evolving in a rapid pace new discoveries are made almost daily. HairDX is committed to providing the latest in genetic discoveries to physicians and their patients.
Finasteride is a synthetic anti-androgen (type II 5-alpha reductase inhibitor) used for treatment of male pattern hair loss (androgenetic alopecia) and benign prostatic hyperplasia (BPH).
Finasteride Response
Recently, several peer-reviewed and published studies discovered a significant association between specific variations of the Androgen Receptor (AR) gene and the likelihood that a man will respond to finasteride therapy for the treatment of androgenetic alopecia (1-3).
A study conducted by Sato et al in 2008 (1) examined the CAG repeat in the first exon of the Androgen Receptor gene in 178 men treated with finasteride (1mg daily) for a period of 48 weeks. The study only included men that developed AGA during the past 10 years and were classified using the Norwood-Hamilton scale as either a II, III, IV, or a V. Sato et al observed a significant correlation between finasteride response and the CAG repeat length of the subjects. Approximately 70% of the men that experienced a great response (a score of 7 in a standardized 7 point global photography scale assessed by an expert panel (4)) to finasteride had a CAG repeat length less then 22 while among men that had a slight response (a score of 5) to finasteride approximately 70% had a CAG score above 22.
A similar study by Wakisaka, et al (3) observed a correlation between the shorter CAG and GGC repeats in the first exon of the AR gene and finasteride response in 488 AGA patients.
The HairDX (RxR) genetic test for finasteride response and BPH provides a physician with their patient’s CAG repeat length score and allows the physician to compare the results to the current scientific literature.
In general, a shorter CAG repeat length (<22) is associated with a greater likelihood that the patient will experience a significant benefit by using finasteride for the treatment of AGA.
Figure 1 depicts the results of the Sato et al study for men that experienced subtle, moderate, and great response.
Figure 2 depicts the degree of improvement associated with subtle, moderate, and great response.
Benign Prostatic Hyperplasia (BPH)
Several studies have shown correlations between AR CAG repeat lengths and an increased risk of developing BPH. Two of these studies conducted in the U.S. had primarily Caucasian patients(9,10), while another study was conducted on a Japanese population(11).
Studies conducted by Giovannucci, et al (9,10) examined subjects from the Health Professionals Follow-up Study and the Physician’s Health Study. The CAG repeat length was determined in 2200 patients. The studies included patients who had clinical signs of enlarged prostates or surgery for BPH. Patients with a CAG repeat length ≤ 19 had a 60% chance of developing BPH by the age of 60. While patients with a CAG repeat length ≥ 25 had a 60% chance of not developing BPH by the age of 60.
A similar study was conducted by Mitsumori, et al (11) examining 176 BPH patients and 41 controls. The study included patients who had open prostatectomies and controls who had no clinical signs of BPH. Patients with a CAG repeat length ≤ 22 had a 60% chance of developing BPH by the age of 60. While patients with a CAG repeat length ≥ 23 had a 60% chance of not developing BPH by the age of 60.
References
1. Sato et al. Correlation between Polymorphic CAG-Repeats in the Androgen Receptor Gene and Therapeutic Efficiency of Finasteride in Androgenetic Alopecia. Skin Surgery: 17(2); 80-86, 2008
2. Sato et al. Polymorphic CAG Repeats in Androgen Receptor Gene And Their Implication in Androgenetic Alopecia. Skin Surgery: 2006
3. Wakisaka et al. Effectiveness of Finasteride on Patients with Male Pattern Baldness Who Have Different Androgen Receptor Gene Polymorphism. J Investig Dermatol Symp Proc 10:293 – 294, 2005
4. Kawashima et al. Finasteride in the treatment of Japanese men with male pattern hair loss. Eur J Dermatol 2004; 14: 247-54
5. Abdel-Wahab et al. Influence of Number of CAG Repeats on Local Control in the RTOG 86-10 Protocol. American Journal of Clinical Oncology: Volume 29(1) February 2006 pp 14-20
6. Sigrid v. Eckardstein et al. CAG repeat length in the androgen receptor gene and gonadotrophin suppression influence the effectiveness of hormonal male contraception. The Clinical Journal of the Clinical Endocrinology. Volume 57 Issue 5, Pages 647 - 655
7. Ennis et al. The CAG repeat polymorphism within the androgen receptor gene predicts biochemical disease-free survival in patients treated with androgen deprivation and conformal external beam radiotherapy. American Society of Clinical Oncology. 2005 Prostate Cancer Symposium
8. Devi Mittal et al. Role of an Androgen Receptor Gene Polymorphism in Development of Hormone Refractory Prostate Cancer in Indian Population. Asian Pacific Journal of Cancer Prevention, Vol 8, 2007
9. Giovannucci, E, et al. The CAG repeat within the androgen receptor gene and benign prostatic hyperplasia. Urology. 53(1); 121-5, 1999.
10. Giovannucci, E, et al. CAG repeat within the androgen receptor gene and incidence of surgery for benign prostatic hyperplasia in U.S. physicians. Prostate. 39(2); 130-4, 1999.
11. Mitsumori, L, et al. Androgen receptor CAG repeat length polymorphism in benign prostatic hyperplasia (BPH): correlation with adenoma growth. Prostate. 41(4); 253-7, 1999.
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