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Department of Gynaecology and Obstetrics (E.L.A., T.B.H.), Andrology Laboratory, Rikshospitalet University Hospital, N 0027 Oslo, Norway; Department of Molecular Medicine (A.N.), Karolinska Hospital, SE 171 76 Stockholm, Sweden; Fertility Centre (A.G., K.B.L., Y.R.) and Department of Urology (K.B.L., Y.L.G.), Malmö University Hospital, Lund University, SE 205 02 Malmö, Sweden; and Cancer Registry of Norway (T.G.), N 0310 Oslo, Norway
Address all correspondence and requests for reprints to: Elin L. Aschim, Andrology Laboratory, Department of Gynaecology and Obstetrics, Rikshospitalet University Hospital, N-0027 Oslo, Norway. E-mail: elaschim{at}biokjemi.uio.no; or Yvonne Giwercman, Malmö University Hospital, Entrance 46, floor 4, SE 205 02 Malmö, Sweden
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Abstract |
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 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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In patients with hypospadias, the phenotype ranges from a slight anomaly, in which the urethral orifice is on the ventral side of the glans (glanular hypospadias) via a penile form to a third subtype (penoscrotal hypospadias) in which the orifice is in the perineum, often combined with a curvature of the penile shaft (chordee). The embryological events underlying these three subtypes of hypospadias differ (3), and different pathogenetical mechanisms cannot be excluded.
The development of internal male genitalia is testosterone (T) dependent. In contrast, 5
-dihydrotestosterone, which is the potent metabolite synthesized from T by the enzyme 5-reductase 2, is essential for normal external masculinization, including proper localization of urethral orifice, as well as development of the prostate. The X-linked androgen receptor (AR) mediates the biological effects of both T and 5-dihydrotestosterone. Thus, a functional AR is an absolute requirement for complete masculinization. Any event that impairs androgen production or normal function of the AR gene may result in undervirilization of male fetuses (4). Because of the pivotal role of the AR in male sex differentiation, the AR gene has been extensively examined in patients with hypospadias. Mutations in the AR gene have occasionally been identified but do not seem to be a frequent cause of this genital malformation (5, 6, 7, 8).
Normal testicular descent is mediated through swelling of the gubernaculum testis. Androgens are believed to play an important role in this process (9), although their role in the development and function of gubernaculum is not completely resolved. Few studies have systematically examined the question of testicular descent in cases with the androgen insensitivity syndrome, caused by mutations in the AR gene, although subjects with this disorder are known to present with the gonads intraabdominally or in an inguinal position. In a report on 16 children with complete or partial androgen insensitivity syndrome as well as two subjects with androgen deficiency (10), 35 of 36 testes were found at or beyond the inguinal ring, leading to the conclusion that the transabdominal phase of testicular descent is independent of androgens, whereas sufficient androgen action is required for the testes to descend through the inguinal canal into the scrotum. However, mutations in neither the AR gene nor the 5-reductase type 2 gene have frequently been found in patients with isolated cryptorchidism (11, 12, 13).
The AR is highly polymorphic due to a glutamine repeat, encoded by (CAG)nCAA and a glycine repeat, encoded by (GGT)3(GGG)(GGT)2(GGC)n, commonly referred to as the CAG and GGN repeat, respectively. Abnormal expansion of the CAG segment to 44 repeats, which is known to reduce AR function both in vivo and in vitro (14, 15), has been found in one patient with hypospadias (16). A more modest expansion of CAG repeat lengths, although within the normal range (approximately 10–30), has also previously been reported in 78 males with varying undermasculinization including hypospadias (17). The authors reported that the mean number of CAG residues and the odds ratio for having 23 or more CAG as opposed to 22 or less CAG increased with the severity of the undermasculinization. The undermasculinized men were also found to have higher odds ratio for having a high number of CAG repeats (more than 27). Most of the patients had penoscrotal hypospadias, and in most cases other features of undermasculinization in addition to hypospadias were also noted. These findings could not be confirmed in a more recent study of 21 patients with hypospadias, the majority having additional genital abnormalities (18).
The CAG repeat length has also been assessed in males with cryptorchidism, but no association between CAG repeat length and undescended testes has been found (19, 20).
Although the polymorphic GGN region of the AR also plays a role in the receptor function (21), studies on this polymorphism in relation to hypospadias or cryptorchidism are still lacking.
The aim of this study was therefore to investigate whether isolated hypospadias and cryptorchidism are associated with any of the polymorphisms in the AR gene. For the former condition, the data analysis was performed for the mixed group as well as the three subgroups separately, taking into account possible differences in the pathogenesis of the glanular, penile, and penoscrotal subtypes.
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Subjects and Methods |
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During the period May 2000 to February 2001, 305 men under compulsory medical examination for military service were enrolled in a study on reproductive function in the general population (22). Because the AR gene is located on the X-chromosome, to exclude any impact of ethnic variation, genotyping was performed only in men with Swedish mothers (n = 220). All participants were asked about their reproductive history, including genital malformations. They underwent a physical examination, and blood samples were drawn for subsequent DNA analysis. All men presented with pubic hair Tanner stage VI and genital development Tanner stage V, which indicated that the pubertal development of their genitalia was completed. Nine subjects with history of cryptorchidism and one with hypospadias were excluded, the total number of controls thus being 210.
Hypospadias
Fifty-one Caucasian boys referred for surgery due to isolated hypospadias were also assessed. Before molecular investigation, the subjects were divided into three subtypes, according to the position of the urethral orifice and degree of chordee, by one investigator (A.N.). The presence of chordee indicates a more proximal origin of the lesion than the mere position of the orifice (23). The classification of these individuals was glanular, penile, and penoscrotal hypospadias.
Cryptorchidism
Nine men among the military conscripts who reported cryptorchidism were included as subjects. In addition, leukocyte DNA was obtained from 14 men with self-reported cryptorchidism, selected among 81 consecutive men seeking medical advice due to infertility and sperm counts less than 5 x 106/ml in two consecutive samples. Also in this subgroup, only those with Swedish mothers were included.
Informed consent was collected from all subjects or their parents, according to protocols approved by the ethical review boards of Karolinska Institute and Lund University.
Analysis of AR gene polymorphisms
Analysis of AR gene polymorphism was performed according to Lundin et al. (24). Briefly, genomic DNA was prepared from peripheral leukocytes, and the CAG and GGN repeats were amplified by PCR for 40 cycles in a 25-µl incubation mixture containing 50 ng DNA; 0.5 µmol/liter flanking primers; 1.5 mmol/liter MgCl2; 200 µmol/liter dATP, dCTP, dTTP, and dGTP (Roche Diagnostics, Bromma, Sweden); 45 mmol/liter KCl; 10 mmol/liter Tris-HCl (pH 8.4 at 70 C); and 0.5 U Dynazyme DNA polymerase (Finnzymes Oy, Espoo, Finland). For GGN analysis, 0.3 µmol/liter of primers, 2.5 mmol/liter MgCl2, and a mixture of 100 µmol/liter dGTP and 100 µmol/liter 7-deaza-dGTP (Roche Diagnostics) instead of 200 µmol/liter dGTP were used. Each amplification cycle included denaturation at 96 C for 1 min and primer annealing for 1 min at 58 and 56 C for the CAG and GGN repeat, respectively. Primer extension occurred at 72 C for 5 min, with an initial denaturation step at 96 C for 3 min and a final extension step at 72 C for 7 min.
One microliter of each PCR product was used for subsequent nested amplification. Nested PCR products were purified using JETPURE PCR purification kit (Genomed GmbH, Bad Oeynhausen, Germany) according to protocol provided by the manufacturer. Approximately 30 ng of the purified products were used in a sequencing reaction with the CEQ Quickstart kit (Beckman Coulter, Bromma, Sweden). Samples were analyzed externally on a CEQ 2000XL (Beckman Coulter) sequencing gear.
Statistical analysis
Because in vitro and in vivo data indicate a decreasing transactvating activity of the AR with increasing CAG length (15), the numbers of these repeats in different groups of patients and controls were compared by Mann-Whitney U test. For the GGN repeats, the relationship between the length and function is less well established. Therefore, apart from intergroup comparison by Mann-Whitney U test, Fisher’s exact test was applied to compare the proportions of subjects with the most common repeat numbers (23 and 24 or more). All statistical tests were two sided. P < 0.05 was considered statistically significant.
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Results |
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In all study groups, by far the most common GGN alleles were 23 and 24 GGN, although their distributions differed. Eight different GGN alleles were found among patients with hypospadias, whereas patients with cryptorchidism had only two, 23, and 24 GGN. No statistically significant differences between the whole group of subjects with hypospadias and controls were found regarding median lengths (Table 1
). GGN numbers were found to be significantly higher (median 24 vs. 23; Table 1) among both subjects with penile hypospadias (P = 0.003) and those with a history of cryptorchidism (P = 0.001), compared with controls. In addition, the GGN numbers among subjects with penile hypospadias were significantly different, compared with the two other subgroups of hypospadias combined (P = 0.018).
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). This difference, although only borderline statistically significant, was also found when comparing the penile with the other two subgroups of hypospadias (32%, n = 21 vs. 55%, n = 12) (P = 0.056). The GGN 24 or more alleles were also more frequent than GGN = 23 in the whole group of men with cryptorchidism (65%, n = 15 vs. 35%, n = 8), compared with controls (P = 0.012) (Fig. 1). The same genetic pattern was also found in the two subgroups of men with cryptorchidism, military conscripts (67%, n = 6 vs. 33%, n = 3), and infertile men (64%, n = 9 vs. 36%, n = 5), however, only reaching the level of statistical significance for the latter when compared with controls (P = 0.085 and P = 0.049, respectively).
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The median CAG repeat length varied from 21 to 23, but the differences were not significant between any of the groups studied and the controls (Table 1
). In the patients with a history of cryptorchidism as well as those with penile hypospadias, the CAG lengths did not differ between those with 23 GGN and subjects with GGN number of 24 or more (data not shown).
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Discussion |
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The finding of an identical switch in the GGN repeat lengths in patients with penile hypospadias as well as in those with a history of cryptorchidism indicates that our results point to true biological associations rather than being chance findings. Androgens are known to play a crucial role for the development of male external genital organs as well as the testicular descent, and previous studies have pointed to partly shared etiology of these two conditions (25).
Evidence from familial subjects has supported a genetic cause of cryptorchidism. To date, mutations in the AR and 5-reductase type 2 genes, both involved in androgen action, have been found to account for only a few cases of isolated congenital malformations of male genital organs. Recently based on animal studies, the INSL3 gene and its receptor Lgr8/Great were suggested candidate genes for cryptorchidism (26, 27, 28). Mutations in the INSL-3 gene or its receptor were reported in eight of 81 infertile men with a history of cryptorchidism (29). However, similar results have not been found in previous studies (30, 31). Therefore, the possible genetic background of hypospadias and cryptorchidism still remains unresolved. Epidemiological trends might indicate a time-related increase in the incidence of both hypospadias and cryptorchidism (32), and it has been suggested that both conditions are manifestations of TDS due to abnormal hormonal milieu in the fetus, combined with a certain genetic predisposition (2, 33). It was suggested that widely used industrial and agricultural chemicals acting as endocrine disrupters might have a deleterious effect on normal male sexual differentiation (32, 33). However, the genetic factors making an individual more susceptible to adverse effects of the environment and/or lifestyle on male reproductive function have not yet been identified. Our findings point to the AR as one of the possible candidate genes.
Despite the alteration in the distribution of the GGN lengths among subjects, they were still within the range found in controls. Therefore, it can be hypothesized that any increase in GGN length above the most common length of 23 causes a slight impairment of AR function, which, combined with insufficient function of the Leydig cells and/or increased exposure to environmentally derived antiandrogens, leads to undervirilization of male genital organs. The significance of the GGN repeats on the function of the AR has previously been demonstrated (21). Likewise, it has been shown that small changes in the length of the CAG trinucleotide length, although within the normal range, can cause variations in androgen action (15). In our material, the patient groups with GGN length of 23 and those with 24 or more repeats did not differ regarding the CAG length; hence, differences in CAG numbers due to linkage disequilibrium with GGN cannot explain the results of the study. However, to provide more evidence for our hypothesis, the impact of small changes in GGN length on the function of the receptor still remains to be shown in vitro.
It is notable that only subjects with penile hypospadias differed from the controls regarding the GGN length. This classification, based on clinical observations, was performed a priori by an experienced investigator without any knowledge of the genotype of the patients. Our findings might indicate that the different subtypes of hypospadias could differ with respect to their etiology and pathogenesis. This finding is in agreement with the available data on the embryological development of external male genital organs. Penoscrotal hypospadias arise due to failure in merging of the labioscrotal folds, whereas the penile subtype is caused by failure of the two urethral folds to close over the urethral plate. The third variant, glanular hypospadias, is associated with disturbed canalization of the glans penis (3).
One of the weaknesses of the study was the fact that the diagnosis of cryptorchidism was based on history taking and not on the hospital recording. However, we believe that any misclassifications would introduce a nondifferential bias and result in an underestimation of the association with cryptorchidism, rather than produce a false-positive result.
It could also be questioned whether the aberrant distribution of GGN repeat lengths among patients with a history of cryptorchidism recruited among the infertile men was due to this congenital malformation or was rather associated with the low sperm counts. However, in the whole group of 81 men with infertility and sperm counts less than 5 x 106/ml, the distribution of these trinucleotide lengths did not differ from the distribution in the general population of Swedish males (24). Although a statistically significant difference in GGN lengths, compared with controls, was found only for the infertile men with a history of cryptorchidism, the distribution was identical among the conscripts with previous maldescent. The lack of statistical significance was due to low sample size (type II error). In addition, by restricting the selection of subjects as well as controls to Caucasians, we reduced a possible impact of interethnic genetic diversity on the results of this study.
In conclusion, we found a significantly increased proportion of individuals with AR gene GGN trinucleotide length of 24 or more among patients presenting with penile hypospadias and those having a history of cryptorchidism. We propose that a slight decrease in AR function caused by expanded GGN, compared with the most common length found in the Caucasian population, combined with a relatively hypoandrogenic endocrine milieu in the fetus may predispose to the development of these congenital abnormalities of male genital organs.
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Footnotes |
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Abbreviations: AR, Androgen receptor; T, testosterone; TDS, testicular dysgenesis syndrome.
Received February 16, 2004.
Accepted July 21, 2004.
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References |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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-reductase type 2 genes in Japanese males do not appear to be associated with cryptorchidism. Fertil Steril 78:330–334[CrossRef][Medline]
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