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Cytogenetic Testing in Pregnant Women Essay

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Updated: Sep 11th, 2022

Case description

This case presents a medical condition (obtained through invasive testing and prenatal karyotyping) of a 30-year-old mother who is presently at 25 weeks of gestation; previous records show triploidy, a small fetus, and an early onset of Intrauterine-Growth-Restriction (IUGR). The fetus’ karyotype has been known to be (46, XX, del (4) (p 14), and it suffers from Wolf-Hirschhorn syndrome. The task in this case, therefore, is to present a discussion of the clinical phenotype for this fetus and as well give counsel to the expectant family.

Generally speaking, prenatal karyotyping and diagnostic genetic testing has been very useful in assessing pregnancies that are vulnerable to genetic disorders and which are as a result of ages of mothers, known family medical records, clearly defined screened results, as well as ultrasonographically defined fetal abnormalities. Conducting prenatal diagnostics is aimed at revealing existent abnormalities in the chromosomes of the fetus; if this is not checked, it will result in severe harm to the fetus; this equally prepares the parents adequately on how and what to do during and after the pregnancy (Hsu, 2010).

For a pregnancy that is in its 25th week, an earlier chorionic villus sampling would have been conducted in the 10th or the 11th weeks of the gestation through transabdominal/transcervical alternatives (or the recently preferred amniocentesis) is supposed.

Clinical Significance for the Fetus

A syndrome could be said to be a dominant expression of a particular clinical condition in a reoccurring state which is supposed to have been caused peculiarly. For a majority of known syndromes, it has been known that their occurrence is largely based on imbalances of the structure of chromosomes. The presented clinical condition of Wolf-Hirschhorn in our study case, like the Cri-du-Chat syndrome, is a clear manifestation of contiguous-gene-syndromes (CGS) that is linked with growth abnormality and some form of mental retardation (MR) caused primarily by chromosomal terminal deletions. A specific way through which insight is gained into the molecular pathogenesis of CGS is through the collection of patients who have closely related phenotypes whereas they have imbalanced variable sizes. According to Hook:

‘The identification of the minimal region of overlap associated with a specific phenotypic feature enables the localization of the genes of that pathology’ (Hook, 1992, p.102).

The method noted by Hook is known as genotype-phenotype-correlations and is one of the earliest pieces of evidence for mapping Cri-du-Chat syndromes. Studies from postnatal diagnosis have equally reviewed a link between subtelomeric regional imbalances and the consequent idiopathic MR. As a result, the use of subtelomeric screening together with evaluated recommendations on patients who have difficult MR but normal karyotype is emphasized. According to Hagerman:

‘Previous studies suggested that for fetuses with ultrasound abnormalities and a normal karyotype, additional screening for submicroscopic imbalances can be relevant for diagnosis and prognosis’ (Hagerman, 2002, p.89).

The conditions identified in our study case are considered below to enable more appropriate counseling of the family.

Triploidy

This is known to be frequently occurring in 2 or 3% during human gestations. The anomaly usually results during early spontaneous abortions, however, at times it continues through the entire fetal period, and results in an affected infant’s birth. Triploidy could be a consequence of digyny (an extra haploid-set gotten maternally) or diandry (which is an extra haploid-set obtained from the father). Being predominant, however, the occurrence of digenic triploidy in a fetus could be up to very high percentages; diandry is responsible for about 50.05 – 60.10% of known cases of early impulsive triploid abortions (Dobzhansky, 1970; Dobzhansky, 1981; Lamed, 2010). For a particular study conducted by Hagerman, it was reviewed that:

Two distinct phenotypes observed in triploid fetuses showed an association with parental origin: 1) the diandrous phenotype was characterized by normal sizes or mildly growth retarded fetus with normal adrenal glands and is associated with an abnormally large cystic placenta with histological features known as partial hydatidiform mole, 2) the digynic phenotype was characterized by an asymmetric intrauterine growth restriction, marked adrenal hypoplasia, and a very small non-molar placenta (Hagerman, 2005, p.208).

The significance of the above-cited to our case of study is that whereas there may be an exhibition of diverse congenital anomalies in triploid fetuses, including total syndactyly of 3rd or 4th fingers, toe syndactyly, non-coherent cardiac/genital conditions, brain/urinary path anomalies, there would not be any significant differences in the appearance of diandrous and digenic fetuses. Equally, the variations are not identified with clear growth differences; this suggests that the differences are developed mostly during the later part of gestations. Prenatally recognized triploidy during gestation, especially the ones that are associated with partial-hydatidiform moles found through placental invasive testing, is of high importance based on the fact that the expectant mothers are under pre-eclampsia risks as well as have higher chances to have consistent trophoblastic diseases.

Del 4p (Wolf-Hirschhorn) Syndrome

Wolf-Hirschhorn syndrome (usually referred to as WHS) is a form of MR syndrome as well as multiple-congenital anomalies (Schinzel, 2001). The medical condition is known to occur once in every 50,000 births- where the predilection of females stands at a ratio of 2 against 1. In any case, there is the possibility that the noted rate as stated above could be underestimated in terms of missed-diagnosed frequencies that may be as a result of limited or total absence of cytogenetic analyses. Studies have reviewed that:

‘The disorder is caused by partial loss of material from the distal portion of the short arm of chromosome 4. The minimal deleted segment causing the phenotype is 4p16.3’ (Sherman, 2002).

Whereas a majority of persons (up to 75.10%) are found to have a de-novo deletion (Holmes, 1987) that is based on a preference from the father (Gardner and Sutherland, 2004), nearly 12.05% of any given population naturally has a sort of abnormal chromosomes (an example is ring 4). Equally, almost 13.0% has a 4p16 deletion which could be inherently unbalanced rearrangements in chromosomes that are rearranged from parents with balanced rearrangements. Research conducted by Battaglia reviewed that:

‘The most striking features of del 4p are the typical “Greek warrior helmet appearance of the nose” (i.e. the broad bridge of the nose continuing to the forehead), pre and post-natal growth delay, congenital hypotonia, mental retardation and seizures’ (Battaglia, 2005).

In accordance with a number of records, epileptic seizures have been one basic clinical challenge associated with WHS patients when they are below age 5 (Gorlin and Levin, 1990). The seizures ordinarily would start before they turn age two- but there could be severe instances even at the ages of nine or ten months. These could be clonic/tonic, unilaterally constituting or not constituting any form of secondary generalization, could be generalized in terms of clonic-tonic right from the beginning.

Counsel to the Family

From the knowledge gathered so far, the noted seizure in the WHS could be appropriately regulated through the use of valproate (singularly or in a combination with ethosuximide). For a few parents, the importance of an addition of a benzodiazepine can not be overemphasized. The significance of this to the parents is that whereas there may be an exhibition of diverse congenital anomalies in triploid fetuses, there would not be any significant differences in the appearance of diandrous and digenic fetuses.

Another Case

This case presents a 30 years old mother at 13 weeks gestation whose fetal statistics include 1:72 risk for Trisomy 21 on first trimester combined screening (FTCS), and the karyotype for the fetus is (46, xx, t (1; 8) (q 25; q 21,2)), reciprocal translocation. The task, in this case, is, therefore, to discuss the clinical significance (clinical phenotype) for the fetus and bring useful counseling issues for the family.

The karyotype for the fetus is (46, xx, t (1; 8) (q 25; q 21, 2)) expresses that each of the fetus’ cells constitutes 46 chromosomes and the XX indicates that the fetus is female with a chromosomes 1 and 8 reciprocal translocation balance. There is equally a swapping between 1q25 to 1q and 8q21, 2 to 8- however, there is no gain/loss in chromosomes for the fetus. Generally, the occurrence of reciprocal translocation balances, an indication of fragmental DNA swapping, has been placed at 1: 500 ratios, globally. There would usually be no defined symptoms and no gains or losses in chromosomes. But in very rare cases, symptoms have been known to occur after the child is born, particularly if the child had over 2 varying chromosomal involvement. Studies have supposed the occurrence to be a result of disruption of very significant genetic materials at breakpoints (Dobzhansky, 1951). For children whose reciprocal translocation balances are from symptomless parents, it is expected that there should be no symptoms for such children.

The clinic conditions presented in our case of study are discussed below:

Trisomy 21 (Down’s) Syndrome

Trisomy 21 syndrome (also referred to as Down’s syndrome or DS) has been known to be an incident in at least one out of each 650 or at a maximum of one in every thousand births where the child survives. It has been found to be closely linked with a condition regarded as triplication of chromosomes-21 and occurs in about 95.0% of clinical cases studied; among studied cases, about 4.0% have chromosomal translocations and a percentage has mosaic trisomic cell line (Dobzhansky, 1951). Jorde et. al., has noted that:

‘The full phenotype appears to manifest when band 21q22 is triplicated, sub-band 21q22.12 being the most critical’ (Jorde et. al., 2003, pp.88-94).

Studies conducted by Gorlin and Levin placed the occurrence of seizures in trisomy 21 syndrome at approximately 5.0-10.0% (Gorlin and Levin, 1990). In any case, evidence about the relationship between age and epileptic incidences has continually expressed that the condition climaxes at the age of 12 months but could continue until the individual turns forty or fifty years of age (Eugster, et. al., 1997). The earliest climaxing point when epilepsy is expressive can be lined with clinical complexities in the earlier part of life (Smith and Berg, 1976), whereas the climax point that comes after happens to take place at the same time when there is development in the transformation of neuropathology, such as the Alzheimer-likes. Several forms of seizures could take place in Down’s syndrome but GTC has been known to be dominant among reported cases (Smith and Berg, 1976). According to Bower et. al:

‘Infantile spasms (IS) in DS are 8-10 times more common than in the general population (Bower et.al., 1967).

Infantile spasms prognosis is ordinarily preferred for controlling seizures as well as for cognition, and remission is achieved through the application of steroids / ACTH with no relapsed seizures. In a case where there is the emergence of new forms of seizures at a later time, they could be (and are mostly) liked with idiopathic age-related variations (Gorlin and Levin, 1990). The only exclusion to these is an instance where there is a perinatal-hypoxic injury (Hook, 1992, p.131).

Age at seizure commencement has been known to be inconsistent and has no etiological-factored evidence apart from Down’s syndrome. A majority of people could have a non-expressive form of epilepsy that is characterized by acoustic/tactile precipitation of all seizures. Even though Lennox-Gastaut syndrome has not been known to occur very frequently, the few instances it occurs it is known to be linked with Down’s syndrome. The occurrence of de novo is particularly very expressive when the child turns 10, however, Lennox-Gastaut syndrome may not accompany the infantile spasms. In the same way, there may never be cases of febrile seizures (Hsu, 2010).

The abnormality in the structure of the brain certainly is very instrumental to epilepsy’s occurrence in Down’s syndrome, especially when associated with other variables including changes in fundamental physiology or neurochemical processes that affect synaptic transmissions (Battaglia, 2005, p.201).

Parental Translocation

Cytogenet happens to be quite uncommon but is a very effective indicator for diagnosing antenatal balances in parental translocations. In a few cases where any form of inversion has been detected, chromosomal abnormalities necessarily require adequate attention. The uniqueness and importance of translocation could be identified through a consideration of a majority of known forms of DS translocations; in this regard, Robertsonian translocation is placed at about chromosomes 14 – 21. For example in our case of study, in a situation where the child has a DS that is a product of translocation, the rearrangement is certain to bring about the occurrence of de nono at least up to 50.0% or even as much as 70.0%. But the possibility for the DS to reoccur in the parents’ progenies may surely be reduced; even though studies have proved the recurrence of an apparent de novo translocation [in 21q; 21q] (Hagerman, 2002). On the other hand, not less than 25-50% of instances of DS which are related to translocation have been traced to at least a parent with the same condition.

Theoretically, the child acquires up to 33.2% of DS from a carrier parent but there are lesser chances for empirical risks. In a situation whereby the father is the carrier of a translocation, chances for the child to acquire this would be within the ranges of 10-15%. The specification in sex differences is noted to be based on abnormalities in the chromosomes of live-birth infants (Holmes, 1987; Schinzel, 2001; Gardner and Sutherland, 2004), as it has been reviewed by studies on amniotic fluids (table below presents data in this regards). Sherman has stated that:

‘Risks are considered similar for other Robertsonian translocations involving chromosome 21, but Robertsonian translocations that do not include chromosome 21 apparently carry much lower risks for unbalanced offspring’ (Sherman, 2002, p.204).

From the table, it can be realized that Robertsonian translocation which is a local condition with healthy individuals clearly possesses 1-2% risk.

Counsel to the Family

Challenges noted with balances in reciprocal translocations are known to impact heavily on carriers- they are more likely to produce offspring with missing or extra chromosomes. These could result in unbalanced translocations and consequently miscarriages for such carriers (Hagerman, 2005). Children who are born by a (46, xx, t (1; 8) (q 25; q 21, 2)) mother will certainly have physical deformations as well as difficulty in learning. The parents of the (46, xx, t (1; 8) (q 25; q 21, 2)) child are advised to ensure that the child does not give birth to a child later than 35 years of age and she should not marry a man with balanced reciprocal translocation as this will increase her chances of having miscarriages or giving birth to children with mental retardation, seizures, structural neurological anomalies, delayed closure of ant fontanelle, poor speech, behavioral problems, and challenges with vision and oculomotility.

Reference List

Battaglia, A., 2005. Wolf-Hirschhorn (4p-) syndrome. In: Cassidy SB, Allanson JE, eds. Management of Genetic Syndromes. Hoboken: John Wiley & Sons Inc.

Bower, B.J., Bower, B.D. and Jeavons, P.M., 1967. The “happy puppet” syndrome. Hoboken: John Wiley & Sons Inc.

Dobzhansky, T., 1951. Genetics and the origin of species. 3rd ed. New York: Columbia University Press.

Dobzhansky, T., 1970. Genetics of the evolutionary process. New York: Columbia University Press.

Dobzhansky, T., 1981. Dobzhansky’s genetics of natural populations. eds Lewontin RC, Moore JA, Provine WB and Wallace B. New York: Columbia University Press.

Eugster, E.A., Berry, S.A., and Hirsch, B., 1997. Mosaicism for deletion 1p36.33 in a patient with obesity and hyperphagia. New York: Oxford University Press.

Gardner, R.J. and Sutherland, G.R., 2004. Chromosome Abnormalities and Genetic Counseling. New York: Oxford University Press.

Gorlin, R.J, and Levin, L.S. 1990. Syndromes of the head and neck. New York – Oxford: Oxford University Press.

Hagerman, R.J., 2005. Fragile X syndrome. In: Cassidy SB, Allanson JE, eds. Management of Genetic Syndromes. Hoboken: John Wiley & Sons Inc.

Hagerman, R.J., 2002. Physical and behavioral phenotype. In: Hagerman RJ, Hagerman PJ, eds. 3rd ed. Fragile X syndrome: Diagnosis, treatment and research. Baltimore: Johns Hopkins University Press.

Holmes, G.L., 1987. Genetics of epilepsy. In: Holmes GL, ed. Diagnosis and management of seizures in children. Philadelphia: Saunders Company.

Hook, E.B. 1992. Prevalence, risks and recurrence. In: Brock DJ, Ferguson-Smith MA, eds. Prenatal diagnosis and screening. London: Churchill Livingstone.

Hsu , T.C., 2010. Human and mammalian cytogenetics: a historical perspective. New York: Springer-Verlag

Jorde, L., Carey, J.C., Bamshad, M.J, and White, L.R., 2003. Medical Genetics. St. Louis: Mosby.

Lamed, P. N., 2010. Fundamentals of Genetics. Ibadan: University Press.

Schinzel, A., 2001. Catalog of Unbalanced Chromosome Aberrations in Man. Berlin- New York: Walter de Gruyter.

Sherman, S., 2002. Epidemiology. In: Hagerman RJ, Hagerman PJ, eds. 3rd ed. Fragile X syndrome: Diagnosis, treatment and research. Baltimore: Johns Hopkins University Press.

Smith, G.F. and Berg, J.M., 1976. Down’s anomaly. Edinburgh: Churchill Livingstone.

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