Genetic sequencing of a patient with Kallmann syndrome plus 5α-reductase type 2 deficiency.

Dear Editor,

Kallmann syndrome (KS) is a phenotypically and genetically heterogeneous disorder featured by hypogonadotropic hypogonadism and congenital hyposmia or anosmia, accompanined with renal dysplasia, hearing loss, and craniofacial defects sometimes. More than 20 genes have been identified causing KS either alone or in combination.

5a-reductase type 2 deficiency (5a-RD) caused by SRD5A2 gene mutation is a rare disease characterized by elevated ratio of testosterone (T) to dihydroteststorone (DHT). The clinical spectrum of 5a-RD is heterogeneous, ranging from the classic phenotype to males with hypospadias and even isolated micropenis. Here, we report a male KS patient accompanied with mild 5a-RD diagnosed from genetic sequencing and clinical analysis.

A 28-year-old male (46, XY) was referred for no secondary sexual characteristics and anosmia. At birth, he had bilateral cryptorchidism, anosmia, and deafness in the left ear. shows the patient's olfactory bulbs and tracts while shows the normal individual. shows his flat pituitary. Bilateral orchidopexy was performed at age five, and there is no prior treatment. The distance between the top of the head to the superior margin of the symphysis pubis was 87.2 cm and from the inferior margin of the symphysis pubis to the sole of the foot was 93.0 cm, and distance between outstretched arms was 187.0 cm. He had bilateral cubitus valgus, and his bone age was 16 years old (). No remarkable frontotemporal hairline recession or acne was noted. Each testicle was in the scrotum without hypospadias. Genital development was Tanner genital stage 1. His pelvic MRI showed prostate dysplasia, mullerian duct cyst (), and seminal vesicles dysplasia (). The MRI of normal seminal vesicles is given in .

Image characters (a) Fat-saturated coronal T2-weighted MR image shows bilateral agenesis of the olfactory bulbs and tracts (arrows). (b) Coronal T2-weighted MR image shows normal olfactory tracts and bulbs (arrows). (c) Sagittal postcontrast T1-weighted image shows a flat pituitary but no lesion (4 mm height, arrow). (d) Direct sequencing of the SRD5A2 gene shows c. 680G> A (p.R227Q) substitution at exon 4 in the patient (top arrow) and the sequence of a normal control subject (bottom arrow). (e) X-ray picture of the patient's left wrist shows a 16-year-old bone age. (f) Sagittal T2-weighted MR image shows a Mullerian duct cyst (the upper arrow) and a dysplastic prostate (the lower arrow). (g) T2-weighted axial MR image shows the patient's bilateral agenesis of seminal vesicles. (h) Axial T2-weighted MR image shows normal seminal vesicles. MR: magnetic resonance.

Normal respond of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) was seen after the subcutaneous injection of triptorelin 100 mg. The results of the triptorelin stimulation test at baseline and 15, 30, 60, 90, and 120 min after injection were LH 0.08, 1.30, 1.48, 1.67, 1.81, and 2.26 (normal: 2–12) IU l−1; FSH 1.02, 2.03, 2.47, 3.03, 3.13, and 4.20 (normal: 1–8) IU l−1, respectively. T, DHT, and T/DHT ratio were 0.32 (normal: 1.58–8.77) μg l−1, 47.58 (normal 57.5–355.0) ug l−1, and 6.78 at baseline, and 4.41 ug l−1, 168.5 ug l−1, and 26.40 after human chorionic gonadotropin (HCG) stimulation, respectively. Other hypothalamic-pituitary-axes’ functions were normal.

The patient was treated with HCG 2000 U i.m. 3 times every week for 9 months, and then human menopausal gonadotropin (HMG) 75 U i.m. was added 3 times a week for another 3 months. Mild improvements in secondary sexual characters are summarized in .

All exons and splice junctions of 23 related genes were screened using Panel or Sanger sequencing. The results were validated by Sanger sequencing. The screened genes were KAL1, FGFR1, FGF8, PROKR2, PROK2, GNRHR, GNRH1, KISS1R, KISS1, TACR3, TAC3, CHD7, WDR11, HS6ST1, SEMA3A, NR0B1, LHB, LEP, LEPR, FSHβ, PCSK1, SRD5A2, and NSMF. SRD5A2 gene variant (c. 680G>A) () was identified in addition to two nonpathogenic variants in KAL1 and GnRH1 (rs808119, rs6185). shows genes information and sequencing results. The failure to find pathogenic genes involved in KS could be due to the mutations mapping outside the coding regions or other candidate genes.

Screened genes and sequencing results

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Both 5a-RD and severe congenital KS could result in low level of DHT in fetus and prostatic dysplasia. When KS co-existed, it is hard to diagnose 5a-RD according to DHT-dependent signs such as facial or body hair, prostate enlargement, and scalp hairline recession. Hence, identification of mild enzyme defect should be based on genetic diagnosis and T/DHT ratio.

Mild 5a-RD as stated above was due to the heterozygous c. 680G>A in exon 4. Makridakis et al.1 reported that the mutant retained 3.2% of normal enzyme activity and slowed the rate of enzyme-catalyzed reaction to 0.06 nmol·l−1·mg−1 (normal, 1.7–2.2 nmol l−1 mg−1). Interestingly, the heterozygous state was found in 5% of their normal Chinese controls. Thus, a remote hypothesis of a dominant effect of some mutations, in particular, cellular environments cannot be completely excluded.2 Since people with the same mutation may have divergent phenotypes even in one family, genetic and functional heterogeneity (due to the presence of SRD5A1 and some interacting factors) should be taken into account. The elevated T/DHT ratio post-HCG stimulation is more sensitive and reliable in diagnosis of 5a-RD3 and helpful to distinguish between androgen insensitive syndrome and other conditions arising from T synthesis defects. The diagnostic cut-off point of T/DHT ratio has not been precisely defined, varied from 3.6 to 18 in diverse ethnic groups pre or after HCG stimulation.456 Obviously, high T/DHT ratio of 26.4 after HCG stimulation is another reason for the diagnosis of mild 5a-RD.

Some authors reported that DHT regulated the expression of genes relevant for normosmia idiopathic hypogonadotropic hypogonadism (nIHH) such as GnRH1, KISS1, and KISS1R and significantly stimulate the migration of FNC-B4 placode in vivo.78 KS might be similar with nIHH in some way. The interaction between KS and 5a-RD need further investigation.

Feyles et al.9 reported that the earlier the orchiopexy performed the better the restoration of spermatogenesis. In 5a-RD, the differentiation from spermatogonium to spermatocyte was defective at an age of 4–6 years, which resulted in a lack of spermatocytes but normal spermatogonium.10 Dysplasia prostate and seminal vesicles epididymis are the primary causes for azoospermia and few semen. Testicular biopsy is an approach to confirm the testicular spermatozoa.

In conclusion, we first reported a male with KS and 5a-RD diagnosed with gene sequencing that will boost the knowledge about geneotype-phenotype connection. If a KS patient had prostate dysplasia, cryptorchidism, unremarkable frontotemporal hairline recession, or a minor response to gonadotropin therapy, SRD5A2 sequencing might be considered.

AUTHOR CONTRIBUTIONS

WJ collected the clinical data, performed the literature search, and drafted the manuscript. LYZ and FCL carried out the molecular genetic studies. ZHL conceived of the study and revised the manuscript. YW, WH, and QQY participated in the follow-up of treatment. All authors read and approved the final manuscript.

COMPETING INTERESTS

All authors declared no competing financial interests.

Table 1

Clinical features and laboratory data