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ORIGINAL ARTICLE
Year : 2017  |  Volume : 21  |  Issue : 4  |  Page : 520-523

Mutational analysis of androgen receptor gene in two families with androgen insensitivity


Department of Genetics, Rainbow Children's Hospital, Sandor Proteomics Pvt Ltd, Hyderabad, Telangana, India

Date of Web Publication9-Jun-2017

Correspondence Address:
Radha Ramadevi Akella
Rainbow Children's Hospital, Road No 10, Banjara Hills, Hyderabad - 500 034, Telangana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijem.IJEM_345_16

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   Abstract 


Background: Androgen insensitivity syndrome (AIS) is a rare X-linked disorder due to mutations in the androgen receptor (AR) gene causing end-organ resistance to the androgenic hormone. Subjects and Methods: Genetic studies were carried out in two families by karyotype and targeted exome sequencing of the AR gene. Results: Two novel missense mutations were identified, p.L822P and p.P392S, in two families with complete androgen insensitivity (CAIS) and partial androgen insensitivity (PAIS), respectively. Both had 46, XY karyotype. The mother was a heterozygous carrier in PAIS and negative in CAIS. These two were novel mutations, reported for the first time, in the AR gene. In silico analysis predicted that both mutations were damaging. We reviewed the various reported Indian mutations in the AR gene. Conclusion: AR gene mutations cause a wide spectrum of disorders from CAIS to male infertility or primary amenorrhea. Early diagnosis is essential for gender assignment and further management, family counseling, and prenatal diagnosis.

Keywords: Androgen insensitivity syndrome, androgen receptor gene, mutation, X-linked recessive disorder, XY karyotype


How to cite this article:
Akella RR. Mutational analysis of androgen receptor gene in two families with androgen insensitivity. Indian J Endocr Metab 2017;21:520-3

How to cite this URL:
Akella RR. Mutational analysis of androgen receptor gene in two families with androgen insensitivity. Indian J Endocr Metab [serial online] 2017 [cited 2019 Nov 17];21:520-3. Available from: http://www.ijem.in/text.asp?2017/21/4/520/207688




   Introduction Top


Androgen insensitivity syndrome (AIS; testicular feminization; OMIM #300068) is a rare X-linked disorder presenting with variable defects in virilization. The incidence is reported to be 1 in 20,000–99,000 in genetic males and 0.8%–2.4% in phenotypic females with an inguinal hernia.[1] A spectrum of phenotypic abnormalities is seen ranging from phenotypic women with complete androgen insensitivity syndrome (CAIS), partial androgen insensitivity syndrome (PAIS), and disorders of sex development (DSW) to normal but infertile men.[2] Lack of virilization can be CAIS or PAIS or mild AIS depending on the residual receptor function. Loss-of-function mutations in the intracellular androgen receptor (AR OMIM #313700) gene result in androgen resistance. Androgen hormone is important for the normal development of internal and external male genitalia in a fetus. XY fetus secretes active androgen hormone and directs the gonad to become a testis (sex determination), leading to a male phenotype. However, when hormone resistance in an XY man or boy occurs, virilization is affected. Complete androgen insensitivity manifests in the form of an XY female. Partial insensitivity cause varying degrees of virilization of the external genitalia from ambiguous genitalia, hypospadias, and cryptorchidism to male infertility.

In the present study, two novel mutations in AIS in two unrelated Indian families were presented, thus expanding the spectrum of mutations in the AR gene with AIS.


   Subjects and Methods Top


Case 1

A nonconsanguineous couple was referred for genetic counseling whose first child was treated for a bilateral inguinal hernia. At 6 months of age, the child was operated for bilateral inguinal masses and histopathology revealed the presence of testicular tissue. No further evaluation was performed. On evaluation, the child was phenotypically a female. Ultrasound examination of the abdomen revealed absent uterus and ovaries. Karyotype of the patient was that of a normal male, 46, XY. A diagnosis of AIS was suspected by clinical presentations, ultrasonography, and karyotype. The present age of the child is 4 years with appropriate growth for age. Targeted exome analysis was performed for the AR gene which revealed a novel pathogenic p.L822P mutation on X-chromosome. Sanger sequencing in the mother was normal indicating a sporadic occurrence of the mutation in the child. None of the family members were diagnosed to have disorders related to abnormal sexual development.

Case 2

A 1-month-old child was seen with a complaint of ambiguous genitalia. This was the first born baby to nonconsanguineous parents, the mother being hypothyroid and on treatment. There was no family history of any affected persons from the maternal and paternal side. The mother of the child had no brothers, and she is the only daughter to her parents. Clinically, the child had micro penis with a penoscrotal hypospadias and cryptorchidism. Plasma follicle-stimulating hormone was 1.9 IU/l and luteinizing hormone was 3.8 IU/l (n < 5). Plasma testosterone at 1 month of age was 11.2 nmol/l (normal 4–10 nmol/l). Karyotype was 46, XY. Mutation analysis for AR gene revealed a novel p.P392S mutation in the AR gene on X-chromosome. Maternal genotype revealed that she is the carrier for the same mutation.

Methods

DNA was extracted from peripheral blood leukocytes to perform targeted gene capture using a custom-made capture kit. The libraries were sequenced to mean >80–100X coverage on Illumina sequencing platform. The sequences obtained were aligned to the human reference genome (GRCh37/hg19) using BWA program and analyzed using Picard and GATK-Lite toolkit to identify variants in the exome relevant to the clinical human reference genome. Annotation of the variant was performed against the Ensembl Release 75 gene model. Clinically, the relevant mutations were annotated using published variants in literature and a set of variant database including ClinVar, OMIM, GWAS, HGMD, and SwissVar.


   Results Top


Targeted mutation analysis of the AR gene revealed a novel homozygous missense mutation in exon 7 of the AR gene on chromosome X that results in the amino acid substitution of proline for leucine at codon 822 (c.2465T>C; p.L822P) [Figure 1] in Case 1 who was a phenotypical female with 46, XY. A novel mutation p.P392S (c.C1174T) was detected in exon 1 (N-ter Domain) in Case 2 who presented with PAIS. Case 1 was sporadic as the mother was negative for the mutation [Figure 2], while Case 2 was inherited where the mother was a carrier for the AR gene. Reviewing the reported mutations in Indian patients, the majority were in the ligand-binding domain (LBD) region [Table 1]. In our patients, one was in LBD and another in N-ter domain.
Figure 1: Integrative Genomics Viewer (IGV) of androgen receptor gene with p.L822P homozygous mutation in Case 1 (by exome)

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Figure 2: Mutation analysis by Sanger sequencing of the mother sample (Case 1) showing the absence of carrier status for p.L822P

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Table 1: Published data on AR gene mutations from India including the two novel mutations from the present cases

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   Discussion Top


AIS is an X-linked disorder, and spontaneous mutations can give rise to disease without any family history. The spontaneous mutation rate in complete AIS is about 30% – a finding consistent with other X-linked recessive disorders such as hemophilia and Duchenne muscular dystrophy.[3] Case 1 is a spontaneous mutation as the mother is tested negative for the mutation. Two-third of cases of AIS are inherited from the mother and one-third of cases come from a spontaneous mutation in the egg. De novo mutations occur at a high rate within the AR gene; a high proportion arises after the zygote stage. Thus, only direct analysis of the underlying mutation of the AR gene in the proband and his or her family can provide the basis for genetic counseling. This is important in counseling as the recurrence of the disease is negligible in sporadic cases. However, in the second family, the mother is a carrier and recurrence is 50% if the fetus carries a 46, XY karyotype.

CAIS presents as inguinal hernia or labial swelling containing testis in female infants. Bilateral inguinal hernias are rare in female infants and should raise the suspicion of CAIS. The incidence of CAIS in females with a bilateral inguinal hernia is 1%–2%.[4] The levels of gonadotropin and testosterone concentrations are less suggestive of hormone resistance when CAIS presents in infancy.[5] Serum testosterone concentrations surge during the first few months of life which is called “mini-puberty” and hence cannot be used to diagnose CAIS in many infants.[6] Concentrations of testosterone and anti-Mullerian hormones are inversely associated during male puberty and is not noticed during the so-called mini-puberty of infancy. Measurement of serum anti-Mullerian hormone in infants not only suggests the presence of testes in complete AIS but also suggests that concentrations are higher with the syndrome than in male infants.[6],[7] This is due to nonexpression of AR in the Sertoli cells of infant testes. This gets exaggerated in CAIS and differentiates it from complete gonadal dysgenesis, a disorder of impaired Sertoli cell function.

The AR gene is localized to the XqI1.12 chromosome and belongs to the nuclear receptor superfamily and has four functional domains encoded by eight exons the N-terminal transactivation domain, a DNA-binding domain, a hinge region, and a C-terminal LBD. Transactivation activity of the AR is induced by the binding of androgen to its LBD, and mutations of the ligand-binding region result in the receptor unable to bind the ligand completely, resulting in CAIS.[8],[9] The reported mutations in CAIS and PAIS in Indian patients are mostly missense mutations distributed throughout the eight exons of the AR gene localized between amino acid residues 688 and 712, 739 and 784, and 827 and 870, which include these two domains, the DNA-binding domains and LBDs, where their functional effect is great because of the ordered structure of these domains.[10] In this study, in the first patient with CAIS, the mutation p.L822P is found in the LBD and the mutation is not associated with the development of Mullerian structures as evidenced by absent uterus and fallopian tubes. In the second patient with 46, XY karyotype, with undervirilized external genitalia and reared as a male, novel mutation p.P392S (c.C1174T) was detected in exon 1 (N-ter domain), who presented with PAIS. The various mutations reported from India are quite heterogeneous with no recurrent common mutation in the AR gene. The majority of the mutations are detected in PAIS; a few are from CAIS and one from primary amenorrhea. However, there are no definite genotype correlations observed between the different phenotypes.[11],[12],[13],[14],[15],[16],[17],[18],[19],[20]

Age of diagnosis of AIS can be anywhere between birth and even before birth to adulthood. Diagnosis is suspected in the fetus when there is a discrepancy between the findings of 46, XY karyotype on amniocentesis and the presence of female external genitalia on prenatal ultrasound examination. Most of the reported cases are adolescents and the present two cases are identified in infancy. Early diagnosis is critical in a newborn with ambiguous genitalia where gender assignment is crucial. A child with DSW phenotype should undergo adequate endocrine and genetic testing for a definitive diagnosis before gender is assigned or surgeries performed. The development of bilateral, inguinal hernia in phenotypic female infants often raises the question of CAIS. When an infant undergoes early gonadectomy, puberty should be induced with estrogen replacement similar to the treatment of Turner syndrome. The advantage of delaying gonadectomy is that puberty occurs spontaneously with growth spurt and breast development without attaining menarche. These individuals are taller compared to those who had early gonadectomy.[21],[22] The risk of gonadal tumor is very low in childhood. Specific analyses in large sample groups suggest a germ-cell tumor risk as low as 0.8%–2%, especially before puberty.[23] In our Case 1, the phenotypic female underwent gonadectomy at 8 months of age and reared as a female. She should be given hormone replacement during adolescence for breast development. In Case 2, the child was assigned male gender with testosterone supplementation and underwent correction of the penoscrotal hypospadias at 3 years of age. Gynecomastia often occurs in adolescence and requires breast reduction mammoplasty.

Genetic counseling

AR mutations are inherited and transmitted in an X-linked manner. Fifty percent of XY-offspring is affected and 50% for an XX offspring is a healthy carrier. In sporadic cases, the risk of transmission is negligible. Germline mosaicism cannot be excluded in any case of de novo mutation of the AR gene, and one should be cautious in counseling these families.


   Conclusion Top


AIS should be diagnosed at an early age and to be differentiated from other disorders of sex. Gender identification is crucial, especially in neonates with ambiguous genitalia. Mutations in the AR gene are highly heterogeneous among Indian patients with AIS.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1]


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