Small Indels in the Androgen Receptor Gene: Phenotype Implications and Mechanisms of Mutagenesis

CONTEXT

Despite high abundance of small indels in human genomes, their precise roles and underlying mechanisms of mutagenesis in Mendelian disorders require further investigation.

OBJECTIVE

To profile the distribution, functional implications, and mechanisms of small indels in the androgen receptor (AR) gene in individuals with androgen insensitivity syndrome (AIS).

METHODS

We conducted a systematic review of previously reported indels within the coding region of the AR gene, including 3 novel indels. Distribution throughout the AR coding region was examined and compared with genomic population data. Additionally, we assessed their impact on the AIS phenotype and investigated potential mechanisms driving their occurrence.

RESULTS

A total of 82 indels in AIS were included. Notably, all frameshift indels exhibited complete AIS. The distribution of indels across the AR gene showed a predominance in the N-terminal domain, most leading to frameshift mutations. Small deletions accounted for 59.7%. Most indels occurred in nonrepetitive sequences, with 15.8% situated within triplet regions. Gene burden analysis demonstrated significant enrichment of frameshift indels in AIS compared with controls (P < .00001), and deletions were overrepresented in AIS (P < .00001).

CONCLUSION

Our findings underscore a robust genotype-phenotype relationship regarding small indels in the AR gene in AIS, with a vast majority presenting complete AIS. Triplet regions and homopolymeric runs emerged as prone loci for small indels within the AR. Most were frameshift indels, with polymerase slippage potentially explaining half of AR indel occurrences. Complex frameshift indels exhibited association with palindromic runs. These discoveries advance understanding of the genetic basis of AIS and shed light on potential mechanisms underlying pathogenic small indel events.

So, and if it is not congenital adrenal hyperplasia? Addressing an undiagnosed case of genital ambiguity

Background

The Congenital Adrenal Hyperplasia due to 21 hydroxylase deficiency is the most common cause of genital ambiguity in persons with XX sexual chromosomes. Genital ambiguity among persons with XY sexual chromosomes comprises diverse and rare etiologies. The deficiency of 17-beta-hydroxysteroid dehydrogenase type 3 enzyme (HSD17B3) is a rare autosomal recessive disorder due to functionally altered variants of the HSD17B3 gene. In this disorder/difference of sex development, the conversion of androstenedione into testosterone is impaired. The appearance of external genitalia of 46,XY individuals varies from typically male to almost female.

Case presentation

We report on a child presenting severe ambiguous genitalia. Due to access constraints, specialized care did not start until the child was 10 months old. Parents are consanguineous and were born in an area of high isonymy that is a cluster for rare recessive diseases. A new homozygous missense variant c.785G > T was found in exon 10 of the HSD17B3 gene.

Conclusions

Researchers-clinicians and researchers-researchers collaborative efforts to elucidate the genetic basis of this disease were critical since this etiologic investigation is not available through the public health system. This case exemplifies the families’ pilgrimage in cases of genital ambiguity due to a rare genetic condition. Recognizing the etiology was the baseline to provide information on prognosis and treatment options, and to shelter family and child doubts and hopes in order to better support their decisions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13052-022-01284-9.

[Profile of patients with genitourinary anomalies treated in a clinical genetics service in the Brazilian unified health system]

OBJECTIVE

To describe the profile of patients with genitourinary abnormalities treated at a tertiary hospital genetics service.

METHODS

Cross-sectional study of 1,068 medical records of patients treated between April/2008 and August/2014. A total of 115 cases suggestive of genitourinary anomalies were selected, regardless of age. A standardized clinical protocol was used, as well as karyotype, hormone levels and genitourinary ultrasound for basic evaluation. Laparoscopy, gonadal biopsy and molecular studies were performed in specific cases. Patients with genitourinary malformations were classified as genitourinary anomalies (GUA), whereas the others, as sex differentiation disorders (SDD). Chi-square, Fisher and Kruskal-Wallis tests were used for statistical analysis and comparison between groups.

RESULTS

80 subjects met the inclusion criteria, 91% with SDD and 9% with isolated/ syndromic GUA. The age was younger in the GUA group (p<0.02), but these groups did not differ regarding external and internal genitalia, as well as karyotype. Karyotype 46,XY was verified in 55% and chromosomal aberrations in 17.5% of cases. Ambiguous genitalia occurred in 45%, predominantly in 46,XX patients (p<0.006). Gonadal differentiation disorders accounted for 25% and congenital adrenal hyperplasia, for 17.5% of the sample. Consanguinity occurred in 16%, recurrence in 12%, lack of birth certificate in 20% and interrupted follow-up in 31% of cases.

CONCLUSIONS

Patients with SDD predominated. Ambiguous genitalia and abnormal sexual differentiation were more frequent among infants and prepubertal individuals. Congenital adrenal hyperplasia was the most prevalent nosology. Younger patients were more common in the GUA group. Abandonment and lower frequency of birth certificate occurred in patients with ambiguous or malformed genitalia. These characteristics corroborate the literature and show the biopsychosocial impact of genitourinary anomalies.

Two Novel Mutations in the Thyroid Hormone Receptor β in Patients with Resistance to Thyroid Hormone (RTH β): Clinical, Biochemical, and Molecular Data

The syndrome of resistance to thyroid hormone (RTH β) is an inherited disorder characterized by variable tissue hyposensitivity to 3,5,30-L-triiodothyronine (T(3)), with persistent elevation of free-circulating T(3) (FT(3)) and free thyroxine (FT(4)) levels in association with nonsuppressed serum thyrotropin (TSH). Clinical presentation is variable and the molecular analysis of THRB gene provides a short cut diagnosis. Here, we describe 2 cases in which RTH β was suspected on the basis of laboratory findings. The diagnosis was confirmed by direct THRB sequencing that revealed 2 novel mutations: the heterozygous p.Ala317Ser in subject 1 and the heterozygous p.Arg438Pro in subject 2. Both mutations were shown to be deleterious by SIFT, PolyPhen, and Align GV-GD predictive methods.

The novel p.Cys65Tyr mutation in NR5A1 gene in three 46,XY siblings with normal testosterone levels and their mother with primary ovarian insufficiency

Background

Disorders of sex development (DSD) is the term used for congenital conditions in which development of chromosomal, gonadal, or phenotypic sex is atypical. Nuclear receptor subfamily 5, group A, member 1 gene (NR5A1) encodes steroidogenic factor 1 (SF1), a transcription factor that is involved in gonadal development and regulates adrenal steroidogenesis. Mutations in the NR5A1 gene may lead to different 46,XX or 46,XY DSD phenotypes with or without adrenal failure. We report a Brazilian family with a novel NR5A1 mutation causing ambiguous genitalia in 46,XY affected individuals without Müllerian derivatives and apparently normal Leydig function after birth and at puberty, respectively. Their mother, who is also heterozygous for the mutation, presents evidence of primary ovarian insufficiency.

Case presentation

Three siblings with 46,XY DSD, ambiguous genitalia and normal testosterone production were included in the study. Molecular analyses for AR, SRD5A2 genes did not reveal any mutation. However, NR5A2 sequence analysis indicated that all three siblings were heterozygous for the p.Cys65Tyr mutation which was inherited from their mother. In silico analysis was carried out to elucidate the role of the amino acid change on the protein function. After the mutation was identified, all sibs and the mother had been reevaluated. Basal hormone concentrations were normal except that ACTH levels were slightly elevated. After 1 mcg ACTH stimulation test, only the older sib showed subnormal cortisol response.

Conclusion

The p.Cys65Tyr mutation located within the second zinc finger of DNA binding domain was considered deleterious upon analysis with predictive algorithms. The identification of heterozygous individuals with this novel mutation may bring additional knowledge on structural modifications that may influence NR5A1 DNA-binding ability, and may also contribute to genotype-phenotype correlations in DSD. The slightly elevated ACTH basal levels in all three patients with 46,XY DSD and the subnormal cortisol response after 1 mcg ACTH stimulation in the older sib indicate that a long-term follow-up for adrenal function is important for these patients. Our data reinforce that NR5A1 analysis must also be performed in 46,XY DSD patients with normal testosterone levels without AR mutations.

46,XX DSD and Antley-Bixler syndrome due to novel mutations in the cytochrome P450 oxidoreductase gene

Deficiency of the enzyme P450 oxidoreductase is a rare form of congenital adrenal hyperplasia with characteristics of combined and partial impairments in steroidogenic enzyme activities, as P450 oxidoreductase transfers electrons to CYP21A2, CYP17A1, and CYP19A1. It results in disorders of sex development and skeletal malformations similar to Antley-Bixley syndrome. We report the case of a 9-year-old girl who was born with virilized genitalia (Prader stage V), absence of palpable gonads, 46,XX karyotype, and hypergonadotropic hypogonadism. During the first year of life, ovarian cyst, partial adrenal insufficiency, and osteoarticular changes, such as mild craniosynostosis, carpal and tarsal synostosis, and limited forearm pronosupination were observed. Her mother presented severe virilization during pregnancy. The molecular analysis of P450 oxidoreductase gene revealed compound heterozygosis for the nonsense p.Arg223*, and the novel missense p.Met408Lys, inherited from the father and the mother, respectively. Arq Bras Endocrinol Metab. 2012;56(8):578-85

Clinical and Laboratorial Features That May Differentiate 46,XY DSD due to Partial Androgen Insensitivity and 5α-Reductase Type 2 Deficiency

The aim of this study was to search for clinical and laboratorial data in 46,XY patients with ambiguous genitalia (AG) and normal testosterone (T) synthesis that could help to distinguish partial androgen insensitivity syndrome (PAIS) from 5α-reductase type 2 deficiency (5α-RD2) and from cases without molecular defects in the AR and SRD5A2 genes. Fifty-eight patients (51 families) were included. Age at first evaluation, weight and height at birth, consanguinity, familial recurrence, severity of AG, penile length, LH, FSH, T, dihydrotestosterone (DHT), Δ4-androstenedione (Δ4), and T/DHT and T/Δ4 ratios were evaluated. The AR and SRD5A2 genes were sequenced in all cases. There were 9 cases (7 families) of 5α-RD2, 10 cases (5 families) of PAIS, and 39 patients had normal molecular analysis of SRD5A2 and AR genes. Age at first evaluation, birth weight and height, and T/DHT ratio were lower in the undetermined group, while penile length was higher in this group. Consanguinity was more frequent and severity of AG was higher in 5α-RD2 patients. Familial recurrence was more frequent in PAIS patients. Birth weight and height, consanguinity, familial recurrence, severity of AG, penile length, and T/DHT ratio may help the investigation of 46,XY patients with AG and normal T synthesis.

Molecular diagnosis of 5α-reductase type II deficiency in Brazilian siblings with 46,XY disorder of sex development

The steroid 5α-reductase type II enzyme catalyzes the conversion of testosterone (T) to dihydrotestosterone (DHT), and its deficiency leads to undervirilization in 46,XY individuals, due to an impairment of this conversion in genital tissues. Molecular analysis in the steroid 5α-reductase type II gene (SRD5A2) was performed in two 46,XY female siblings. SRD5A2 gene sequencing revealed that the patients were homozygous for p.Gln126Arg missense mutation, which results from the CGA > CAA nucleotide substitution. The molecular result confirmed clinical diagnosis of 46,XY disorder of sex development (DSD) for the older sister and directed the investigation to other family members. Studies on SRD5A2 protein structure showed severe changes at NADPH binding region indicating that structural modeling analysis can be useful to evaluate the deleterious role of a mutation as causing 5α-reductase type II enzyme deficiency.