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Congenital Bilateral Absence of the Vas Deferens (CBAVD)

Definition

Congenital bilateral absence of the vas deferens (CBAVD) is the bilateral absence of the vas deferens, frequently associated with agenesis or hypoplasia of the seminal vesicles and, in some cases, other malformations of the urinary tract.

Epidemiology

Unilateral absence of the vas deferens occurs in 0.6–1%. The bilateral form is approximately tenfold less common and accounts for up to 6% of cases of obstructive azoospermia.

Etiology

CFTR variants

Pathogenic variants in the CFTR gene (cystic fibrosis transmembrane conductance regulator) can cause bilateral absence of the seminal vesicles and/or vasa deferentia. Clinical cystic fibrosis is not obligatory; CBAVD is regarded as a minimal manifestation of CFTR-related disease. Clinical cystic fibrosis in men is almost invariably associated with CBAVD or another obstructive seminal tract anomaly. The CFTR genotype in CBAVD is heterogeneous: it may comprise two CFTR variants, often one severe and one mild variant; a single CFTR variant combined with splice variants; or, less commonly, no detectable CFTR variant.

Association with unilateral renal agenesis

Patients with absence of the vas deferens and no detectable CFTR variants have ipsilateral renal agenesis in up to 40% of cases. This results from a developmental disorder of the urogenital ridge, which, depending on its timing and extent, affects the ureteric bud, mesonephric duct (Wolffian duct), and sometimes also the paramesonephric duct (Müllerian duct). Associated malformations of the internal genital organs are possible.

Signs and Symptoms

The vasa deferentia cannot be palpated. Unilateral absence of the vas deferens usually causes no symptoms. Patients with CBAVD have obstructive azoospermia and infertility.

Diagnosis

• Semen analysis: azoospermia and signs of seminal tract obstruction: pH <7, low ejaculate volume, and low fructose.
• Normal hormone profile.
• TRUS: possible absence of the seminal vesicles.
• CFTR variant analysis if the vasa deferentia are not palpable and azoospermia is present. If the patient wishes to have children, CFTR testing of the female partner and genetic counselling are also indicated.
• Abdominal ultrasonography to exclude renal malformations if no CFTR variants are detected.

Treatment of CBAVD

Treatment is necessary only if the patient wishes to have children. Reproduction is possible through surgical sperm retrieval followed by intracytoplasmic sperm injection (ICSI); the increased risk of cystic fibrosis must be considered.

Genetic Counseling

Cystic fibrosis is inherited in an autosomal recessive manner; in Germany, its incidence is approximately 1:2500–1:4000 and the CFTR carrier frequency is 1:25–1:30. In men with CBAVD, the risk of cystic fibrosis in a child conceived by ICSI depends on the CFTR genotype of both partners. If a clinically relevant CFTR variant is identified in the man and the female partner is not genetically screened, the risk is often estimated to be approximately 1:100 (Tüttelmann et al., 2008).

References

Tüttelmann, F.; Gromoll, J. & Kliesch, S. [Genetics of male infertility].
Urologe A, 2008, 47, 1561-2, 1564-7

  Deutsche Version: CBAVD

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