PMDS is one of the rarest causes of disorders of sex development (DSD) with clinical and genetic heterogeneity and is characterized by the presence of a bicornuate uterus, fallopian tubes, and the upper third of the vagina in normally masculinized 46, XY subjects.1 The incidence has not been accurately determined. Since its initial description, the details of more than 250 cases have been published, and variants in AMH and AMHR2 have been identified in these patients. Thus far, few studies from China have reported the variant spectrum and management experiences of PMDS patients. In the current study, we report the clinical experiences and genetic findings of 12 new patients from China.
In our literature review, 56.6% of the included patients presented with bilateral cryptorchidism, 20.8% with unilateral cryptorchidism, known as hernia uteri inguinalis, and 22.5% with TTE (Figure S1). The data were updated and included newly reported patients and our Chinese patients2. However, in the current study, unilateral cryptorchidism present in more than half of the patients, was the most common phenotype. We also found that the position of the testis was flexible and was always reset during laparoscopic exploration, although it was preoperatively detected on the contralateral side of the body (mostly in the groin) by ultrasound (Table 1). It is easy to confuse TTE with unilateral cryptorchidism, and it is possible that there is no need to distinguish them. Moreover, the high flexibility of the testes due to the abnormal mobility of the uterus facilitates their torsion and may lead to uni- or bilateral testicular degeneration.17 The testis of patient 2 was ascertained to be atrophied.
In children, PMDS is usually a surprising finding made during corrective surgery for inguinal hernia or cryptorchidism. Testicular histology is generally performed for diagnosis during the first surgery without therapeutic surgery, and the morphology is usually normal.2 Therefore, preoperative diagnosis is critical and can help to avoid unnecessary testicular biopsy and reoperations. Unilateral or bilateral cryptorchidism is not particularly evocative, although unilateral cryptorchidism with contralateral hernia, particularly TTE, should evoke suspicion. In the present study, the diagnosis was made preoperatively in more than half of the patients. Seven of these patients underwent ultrasound, and one patient underwent gene sequencing. If physical examination and ultrasound show any sign of a testis crossing the body midline, PMDS should be considered. Moreover, preoperative gene sequencing can contribute to an accurate diagnosis when a damaging variant of AMH or AMHR2 is detected.
In our literature review, variants of AMH and AMHR2 were reported in 87.9% of all patients and were approximately equally distributed among the genes coding AMH and its type II receptor, AMHR2. Statistics indicated that AMH presented 78 different variants in 93 families, and 80 different alleles of AMHR2 were discovered in 94 families. In our Chinese patients, mutational analyses revealed possible causative variants in all patients. AMH variants occurred more frequently than AMHR2 variants, consistent with a previous report.2 Variants are known to occur along the entire length of AMH, although exons 3 and 4 are very rarely involved (Fig. 2A). The short C-terminal fragment is a TGF-beta like domain with biological activity. The large N-terminal region is not thought to be essential for activity, but exerts the ability to stabilize the C-terminus,18 and shows nearly 2.5 times the hit of the C-terminus (Fig. 2A). In our study, twelve variants, including eight new variants, were identified in AMH. The c.301G > A (p.G101R) and c.1165G > T (p.E389X) were recurrent in three and two unrelated families respectively. c.301G > A (p.G101R) has been previously described in four families, while c.1165G > T (p.E389X) has been reported in two families. c.1637C > A (p.A546E) was also previously detected in one family. AMHR2 encodes a membrane protein and has 11 exons, which are all affected by variants (Fig. 2B). Only two hits were observed in the transmembrane domain. The protein kinase catalytic domain was more conserved and showed nearly 5 times more hits than the activin types I and II receptor domains. In our Chinese patients, six variants in the AMHR2 gene were found, including five new variants of “uncertain significance (VUS)”. c.160C > T (p.R54C) was previously described in one family.19 Functional studies have not been reported, so further studies are needed to investigate the harmfulness of these variants.
Normally, AMH concentrations are maintained at high levels during childhood and decrease at puberty20. Patients with AMH gene defects show low AMH levels from birth, whereas patients with variants in AMHR2 show elevated AMH levels, indicating insensitivity of the target tissues21. In contrast, patients 3 and 9 with variants in AMH presented increased AMH levels, indicating that the interactions between variants p.(R451H) and p.(G101R) and between p.(S35Qfs*46) and p.(Y483H) might affect hormone bioactivity and not the hormone secretion rate.22
The genotypes of AMH and AMHR2 are not related to the observed phenotypes2,23. The phenotype can differ within the same family and shows no relationship to the type of genetic defect involved. The anatomical abnormalities common to all patients with PMDS result from the failure of the gubernaculum to anchor the testes at the base of the scrotum. The abnormal mobility of the uterus with the testes facilitates their torsion and may lead to uni- or bilateral testicular degeneration17. In the current study, the left testis of patient 1 was located in the left groin, while the testis of his brother, patient 2, was atrophied on the left side. Furthermore, neither laparoscopy nor imaging was able to detect Müllerian derivatives in patient 2, even though he harbored the same variants as his brother with PMDS (patient 1). This suggests highly variable penetrance of the abnormal alleles and/or the existence of other genetic or epigenetic modifiers of gene expression.
The management of PMDS consists of the correction of cryptorchidism to prevent testis degeneration and preserve fertility.2,24 Because of the high mobility of the uterus with the testes, bilateral orchidopexy is recommended, as we performed in the current study. The rate of testicular malignancy is up to 33% in PMDS patients older than 18 years, which is higher than the rate among general cryptorchidism cases. Close follow-up of the testes is necessary with age2.
There is no consensus regarding whether MRs should be excised in PMDS patients. Previous reports have advocated retaining MRs to prevent damage to the vas deferens, considering that MRs present no risk of malignancy25. In the current study, MRs were preserved in eight patients, but complications occurred in five patients. To our knowledge, this is the first study to report the emergence of MR cysts after MR preservation. The cysts were thought to be hydrocolpos caused by the accumulation of fluid due to congenital vaginal obstruction. In our experience, such cysts may decrease in size and remain stable, but long-term outcomes still need to be followed up. Irreducible cryptorchidism occurred in two patients following MR preservation, which may have been due to the mobilization of MRs.
Since 2002, three PMDS patients have been reported to have developed malignancy of MRs originating from the mucosa 3–5. The preferred surgical procedure is to split the uterus in the middle, destroy the mucosal lining, and leave an intact pedicle of the myometrium.24,26,27 This not only releases the testes to the ideal position but also protects the integrity and vascularity of the vas deferens and reduces the chance of malignancy. In the current study, three patients underwent partial hysterectomy, but two of them experienced side effects. One presented the complication of hemorrhage, indicating that complete hemostasis should be noticed. The vas deferens is injured in TTE because it is enclosed in MRs, so surgeons need to improve their surgical techniques and perform dissection carefully. In addition to malignant degeneration, retained MRs are known to cause hematuria, recurrent UTI, stones and voiding disturbances27,28, but these conditions were not noticed in our series.
Infertility is another problem observed in PMDS patients. The possible causes include congenital malformations of excretory ducts, long-term cryptorchidism, and damage to the testicular blood supply or the vas deferens during hysterectomy. In the present study, the incidence of vas deferens malformation was high, occurring in half of the patients. We also noted a high incidence of TM (25%), which may contribute to another cause of infertility.29
Follow-up is extremely important for these patients, especially the monitoring of malignancies of the testes and uterus, with concern for their fertility. Close follow-up of all of our patients continues in our clinic.
Perspectives and Significance
We report 12 new Chinese PMDS patients with 13 novel possible causative variants in the AMH and AMHR2 genes. Bilateral orchidopexy with destruction of the uterine mucosa may be the optimum surgical procedure for PMDS.