Archives of Disease in Childhood 1997;76:529–531 529 Phenotypic diversity in siblings with partial androgen insensitivity syndrome Arch Dis Child: first published as 10.1136/adc.76.6.529 on 1 June 1997. Downloaded from BAJEvans, I A Hughes, C L Bevan, M N Patterson, J W Gregory Abstract Four sites in the steroid binding domain, The androgen insensitivity syndrome is a arginine residues 774, 840, and 855, and valine heterogeneous disorder with a wide spec- 866, appear to have a particularly high trum of phenotypic abnormalities, rang- frequency of mutation and together account ing from complete female to ambiguous for about one quarter of the missense muta- forms that more closely resemble males. tions reported to date.36 Arginine 840 is The primary abnormality is a defective reported to be the site of substitution by either androgen receptor protein due to a muta- cysteine or histidine in multiple patients (three tion of the androgen receptor gene. This and nine patients, respectively). These substi- prevents normal androgen action and thus tutions are both associated with a variety of leads to impaired virilisation. A point phenotypes within the partial form of AIS, highlighting the complexity of the genotype- mutation of the androgen receptor gene 3 aVecting two siblings with partial andro- phenotype relation in androgen insensitivity. gen insensitivity syndrome is described. Indeed, even within a few families with partial One had cliteromegaly and labial fusion AIS considerable phenotypic variability has been reported,78 although most of these and was raised as a girl, whereas the other reports were before mutational analyses of the sibling had micropenis and penoscrotal androgen receptor gene were possible. The hypospadias and was raised as a boy. Both molecular basis of this phenotypic variation has were shown to have the arginine 840 to been investigated in only a few families9 and is cysteine mutation. The phenotypic varia- still not understood. tion in this family is thus dependent on We describe a point mutation of the factors other than abnormalities of the androgen receptor gene aVecting two siblings androgen receptor gene alone. with the partial form of the AIS in a completely ( 1997;76:529–531) Arch Dis Child diVerent manner. One had cliteromegaly and labial fusion and was raised as a girl, whereas Keywords: androgen receptor mutations; androgen insensitivity syndrome; phenotypic diversity the other sibling had micropenis and penoscro- tal hypospadias and was raised as a boy. Both http://adc.bmj.com/ were shown to have the arginine 840 to cysteine Mutations of the androgen receptor gene in mutation. subjects with a 46,XY karyotype give rise to the androgen insensitivity syndrome (AIS). The Subjects and methods syndrome is a heterogeneous disorder with a The family pedigree is shown in fig 1. The wide spectrum of phenotypic abnormalities index case (II.1) was born at 32 weeks’ ranging from complete female to ambiguous gestation by caesarean section weighing 1980 g on October 2, 2021 by guest. Protected copyright. forms that more closely resemble males. The and was noted at birth to have ambiguous primary abnormality is a defective androgen genitalia. The phallus measured 1.5 cm, there receptor protein which prevents normal andro- was a urogenital sinus, a 1 cm blind ending gen action and thus leads to impaired 1–3 vagina, and both gonads were palpable in the virilisation. labioscrotal folds. The karyotype was 46,XY The androgen receptor protein is encoded Department of Child and there was a significant testosterone re- Health, University of by a single gene containing eight exons located sponse (7.5 to >20 nmol/l) to human chorionic 4 Wales College of on the Xq 11-12. Like other members of the gonadotrophin stimulation undertaken within Medicine, Heath Park, steroid receptor family the gene comprises one month of birth. The infant was assigned a CardiV CF4 4XN three functional domains: parts of the N termi- female gender and at 21 months underwent BAJEvans nal end promote the transactivation of certain J W Gregory vulvoplasty, bilateral orchidectomy, and hernio- target genes; a DNA binding domain facilitates tomy. On examination at the age of 9 years she Department of binding of the androgen receptor protein onto had normal external female genitalia. Paediatrics, University promoter regions of specific target genes; and a A younger sibling (II.2) was born two years of Cambridge, steroid binding region is responsible for the later and was noted at birth to have a slightly Addenbrooke’s specificity and aYnity of ligand binding.5 Stud- shortened penis, penoscrotal hypospadias with Hospital, Cambridge I A Hughes ies of AIS to date, mainly in subjects with com- chordee, and a bifid scrotum with both testes C L Bevan plete forms of the syndrome, have identified a palpable. Cystourethroscopy was normal and M N Patterson variety of androgen receptor gene deletions and the karyotype was 46,XY. As he was substan- insertions and a much larger number of single tially more virilised than his sister, he was Correspondence to: base mutations that introduce premature raised as a boy and underwent a Duckett’s Dr Evans. termination codons, amino acid changes, or hypospadias repair aged 14 months. At 7 years Accepted 5 March 1997 aberrant messenger RNA splicing.6 of age his phallus measured 2.5 cm and his 530 Evans, Hughes, Bevan, Patterson, Gregory 12 3tor which is qualitatively abnormal. SSCP I screening of exon G showed a shift in the mobility of denatured PCR segments from II.1 Arch Dis Child: first published as 10.1136/adc.76.6.529 on 1 June 1997. Downloaded from and II.2 when run on a non-denaturing gel (results not shown). Direct sequencing of exon 12G in subjects II.1 and II.2 confirmed the pres- II ence of a point mutation (guanine to adenine) causing a change from arginine to cysteine at amino acid 840 (fig 2). Their mother, I.2, was shown to be a carrier for this point mutation Affected family members (fig 2). Carrier Discussion Figure 1 Pedigree of family with partial androgen This study reports a single amino acid insensitivity and variable phenotype. substitution (arginine to cysteine at position 840) in the steroid binding domain of the scrotum was well developed, although the androgen receptor gene in two patients with testes were palpable in the inguinal canal. partial AIS. This particular codon is reported as one ‘hotspot’ of mutations based on the cur- TISSUE CULTURE AND ANDROGEN BINDING ASSAY rent database of the androgen receptor gene A fibroblast cell line was established from a mutations.6 Table 1 summarises the reported genital skin biopsy sample obtained from II.2 mutations of arginine 840 in relation to the at the time of his operation. Normal control aVected phenotype of the index case where cell lines were established from circumcision suYcient clinical details were available. There specimens. Androgen binding was measured is no consistency in the sex of rearing between using whole cell binding assays as previously aVected families. Within aVected families, 10 described. however, siblings have generally been similarly aVected and raised as the same sex.14–16 There is POLYMERASE CHAIN REACTION SINGLE STRAND one report of a Japanese case where the index CONFORMATION POLYMORPHISM ANALYSIS AND patient was female, but other family members SEQUENCING OF THE ANDROGEN RECEPTOR GENE who had abnormal genitalia were raised as Genomic DNA was prepared from whole boys.17 blood from I.2, I.3, II.1, and II.2 using stand- Our family is unique in showing such a pro- 11 ard methods. The androgen receptor gene found diVerence in the degree of virilisation so was screened for mutations using polymerase that the decision about the sex of rearing was chain reaction single strand conformation clear from the outset in each instance. Such polymorphism (PCR-SSCP) techniques as intrafamilial variance in the phenotypic expres- described elsewhere.12 13 Sequencing reactions sion of an identical single gene mutation http://adc.bmj.com/ were also carried out as previously described13 emphasises the need to approach prenatal using the fmol DNA sequencing system counselling of partial AIS with caution.18 (Promega). Predicting outcome is more certain with com- plete AIS, where within aVected families there Results is no partial form of AIS and hence the sex of The maximum binding capacity and apparent rearing would always be female. An arginine dissociation constant (Kd) for the androgen 855 histidine mutation was reported to result receptor in genital skin fibroblasts from II.2 in complete AIS in one family and a partial AIS on October 2, 2021 by guest. Protected copyright. were 749 × 10–18 mol/µg DNA and 2.9 × 10-10 phenotype in another unrelated family, mol/l (normal range 814 +/− 186 and 0.91 +/− however.15 The androgen receptor is a member − 0.26, respectively, n = 14). This Kd is 3.1 fold of a large family of nuclear transcription factors higher than that in normal subjects. Androgen which are usually activated in the presence of binding at 40˚C decreased to 55% of the value ligand binding to specific pockets in the forma- obtained when the assay was performed at tion of the tertiary protein structure.19 Other 37˚C (normal range +/−16%). The altered examples of dysfunctional transcription factors binding aYnity and thermolability indicate due to a single mutation, but associated with that this cell line expresses an androgen recep- a spectrum of clinical expression, include Figure 2 Sequencing of exon G in subjects I.2 and II.2. The sequencing abnormality seen in II.2 was also detected in II.1 (results not shown). The altered nucleotide is boxed.