Importance of Genetic Testing in Male Infertility

Genetic testing in male infertility

It is estimated that men are responsible for 40-50% infertility cases. Known genetic factors are responsible for 20% of male infertility 30-60% of azoospermia is idiopathic & require factor genetic testing.

2 Important reasons for testing is-

(a)- To identify possible genetic defects with risk transmission to offspring through ART

(b)- To detects genetic disorders importing the ability to obtain spermatozoa through sperm retrieval techniques such as micro TESE etc.

Genetic tests- karyotyping CFTR mutation screening Y chromosome micro detection

Karyotyping- recommended for all men having fetal notice sperm count <5 million &men with non-obstructive azoospermia.

• Chromosomal abnormalities are detected are aneuploidy (e.g.-trisomy) &structured ( e.g.- inversions /translocations)
• Genetic technique

(A) Karyotyping –Giemsa/trypsin staining on metaphase derived from peripheral blood lymphocytes

(B) Molecular genetic testing –FISH&CGH.

Klinefelter syndrome- 47XXY karyotyping most common chromosomal aneuploidy up to 12% of men in azoospermia .

Infertility due to defect in spermatogenesis leading to azoospermia /severe oligozoospermia.

80-90%-47xx4

10-20%- 46×4/47xx4,48xxxy or 48xxyy

Main genetic cause- meiotic nondisjunction

According to ASRM (American society for reproductive medicine)

Men with non-obstructive azoospermia & severe oligozoospermia must be offered high resolution karyotype before using sperm for ICSI.

Y chromosome micro detections (AZF)- micro detections occurs most frequently on long arm of Y chromosome Y q. Y chromosome deleted regions are mapped to 3azoospermia factor (AZF)-AZFa ,AZFb& AZFc.

(1) AZFa detection-sertoli cell only syndrome.

(2)  AZFb detetion- spermatogenic arrest

(3)  AZFc- sectoli cell only syndrome to oligozoospermia

(Residual spermatogenesis – success rate 50-70%)

Technologies used –polymerase chain reaction technique.

CFTR- gene defects & obstructive azoospermia –

CFTR related male infertility is subdivided into following phenotypes:–

• Congenital bilateral absence of vas deferens(CBAVD)
• CBAVD having unilateral renal anomalies
• Congenital unilateral absence of vas deferens (CBAVD)
• Ejaculatory duct obstruction

CFTR gene is on chromosome 7q 31.2 CFTR gene contains 27 axons &three are >2500 mutations repeated ranging from most lethal cystic fibrosis (CF) to mild phenotype CBAVD screening of female partner for CF carrier is essential for calculating accurate genetic risks & offering counseling & treatment option .PGS is recommended when female partner of CBAVD has CFTR mutation .

Algorithm for genetic investigations of male infertility.

                   Azoospermia

Testis                                 testis>10                               testis size< (8-10ml)

Low semen volume         biopsy               biopsy

Low PH                    hypermatogenesis     germ cell at rest     sertoli cell

Absent vas deference Y chromosome   Y micro deletions     C-kit/set

On palpation                   micro deletion   meiotic arrest gene Bcl-W

CFTR gene testing                                                                         ERX

Female partner carrier screening

Genetic counseling.

 

Testis size c 8-10 ml

Low                                                                              (N)or high FSH

FSH /LH/T                                                              FSH receptor mutation

Kallmann syndrome                                            Y micro detections

Meiotic arrest genes

Genetic counselling

Oligospermia-sperm count <5-10 million

Karyotyping

Y micro detecting

AR mutations