Concerning genetics, biographical information includes data such as ethnicity. Although diseases occur in all ethnic groups, some are more frequent in specific populations as compared to others. Therefore, being that prior risk is centered on the couples’ and donors’ ethnic background, residual risk will also be affected. Based on the residual risk of the Counsyl test, donor 2, who is Chinese, had a higher probability of being a carrier for several disorders as compared to donor 1, who is Portuguese.
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Some of the reasons as to why someone might want to utilize egg/sperm donation include the male partner having significant seminal fluid or sperm abnormalities such as azoospermia and severe oligozoospermia. Also, either of the partners having a significant genetic defect.
The punnet square is useful in determining the risk of an offspring having a particular genotype; hence, disease. One of the genotypes of the parent is known, and the Counsyl findings show that both donors do not suffer from cystic fibrosis (CF) –an autosomal recessive disorder (Castellani & Massie, 2014). Therefore, in the case that the untested parent is a carrier, the risk of having a homozygous and heterozygous offspring is 0 and 0.5, respectively.
C – Normal allele; c – Allele with CF mutation
For donor 1, the priori risk of the child is; (
For donor 2, the priori risk of the child is; (
If the untested parent is normal, the risk of having a homozygous recessive offspring is 0, while that of a heterozygous offspring is 0.5. As a result, for both donors, the priori risk of the child acquiring the disorder is ultimately 0.
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The two possible genetic disorders that were selected include the x-linked juvenile retinoschisis (XJR) and autosomal recessive polycystic kidney disease (ARPKD). They were chosen as they had the highest likelihood of being transferred to the fetus (XJR = <1 in 62,000; ARPKD = <1 in 22,000). XJR is described as a degenerative vitreoretinal disorder that is common among young males. It has an estimated incidence of 1:5000-28000 (Silveira, Provenzano, & Soares, 2015).
Its etiology is attributed to mutations in the retinoschisin gene. The gene controls the coding of retinoschisis – a protein providing interaction and adhesion among cells and retinal layers. XJR is characterized by bilateral maculopathy, peripheral retinal elevations, retinal detachment vitreous veils over the peripheral schisis, and vitreous hemorrhage. It manifests in the form of decreased visual acuity (VA) between the ages of five and ten (Silveira et al., 2015). It evolves with advancing visual loss in the first twenty years of life. VA might stabilize until the individual attains the age of 50-60, after which it worsens because of macular atrophy. The VA in young adults is approximately 20/70 (Silveira et al., 2015).
On the other hand, ARPKP is a fibrocystic disorder that occurs mostly in neonates and affects the liver and kidney. It has a prevalence of 1:10,000-40,000 (Hartung & Guay-Woodford, 2014). It is caused by a mutation in the PKHD1 gene, which codes for polyductin or fibrocystin that assists in the differentiation of bile duct, pancreatic duct, and kidney tubules. As a result, the clinical hallmarks of ARPKP are enlarged kidneys with fusiform dilatation of the collecting ducts and congenital liver fibrosis. It is associated with approximately 30% of perinatal deaths (Hartung & Guay-Woodford, 2014). Furthermore, infants that survive acquire progressive liver disease and renal failure, which results in portal hypertension.
With regard to the information collected above, donor 1 is the most suitable for donation. This is because donor 2 had a higher number of genetic disorders in which their residual risk was higher than that of donor 1. Moreover, the priori risk of the child inheriting CF was higher for donor 1. Overall, this suggests that donor 1 is susceptible to a more significant number of genetic disorders that will lead to an increase in the risk of recessive disease inheritance. This negates the objective of carrier screening, which is to help minimize the future risk of the fetus inheriting recessive diseases.
Castellani, C., & Massie, J. (2014). Newborn screening and carrier screening for cystic fibrosis: Alternative or complementary? European Respiratory Journal, 43, 20-23. Web.
Hartung, E., & Guay-Woodford, L. (2014). Autosomal Recessive Polycystic Kidney Disease: A hepatorenal fibrocystic disorder with pleiotropic effects. Pediatrics, 134(3), 833-845. Web.
Silveira, C., Provenzano, J., & Soares, G. (2015). X-linked Juvenile retinoschisis. Revista Brasileira de Oftalmologia, 74(4), 241-243. Web.