Karyotype – Fertility

Conventional karyotyping is indicated in patients being investigated for fertility issues. There is an increased carrier rate of balanced chromosome rearrangements (not detected by microarray) in both male and females in this group of patients. At least 40% of males who carry a chromosome rearrangement have a normal sperm count.

Carrier rates in males are 1.73%, a 4.8 fold increase over background

Carrier rates in females are 0.92%, a 2.6 fold increase over background

Sperm FISH (fluorescence in situ hybridization):

Indications:

  • normal semen analysis but unexplained infertility
  • recurrent pregnancy loss
  • repeated IVF failures

Sperm exhibit chromosome aneuploidy in a low percentage in males of proven fertility. Looking for aneuploidy in the sperm of males whose partners have been unsuccessful with ART (assisted reproductive technologies) can be useful.

This test is also of use in males who have undergone either radio- or chemotherapy to determine whether their sperm had been impacted by the treatment.

Men who are translocation carriers produce chromosomally abnormal as well as normal sperm. The frequency of genetically normal gametes varies greatly (from 20-80% from sperm FISH studies) and this will impact in IVF on the number of failed embryo transfers.  For couples where the male carries a translocation, sperm FISH, which determines the frequency of normal or balanced sperm, may be of use where embryo transfer has been unsuccessful. The literature suggests consideration of donor sperm where the normal/balanced rate is lower than 35%.

Azoospermia:

Males with azoospermia may have cytogenetically detectable rearrangements of the Y chromosome, molecular deletion of the AZF region of Yq or may be carriers of a variant in the Cystic Fibrosis gene that leads to congenital absence of the vas deferens.

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