Some chromosomal abnormalities like Down’s syndrome, Klinefelter’s syndrome, Turner’s syndrome, and metabolic disorders like phenylketonuria, sickle cell anemia, etc. are the fetal disorders can be detected in early pregnancy.
Down’s Syndrome or Mongolism is a genetic disorder with one extra copy of chromosome 21 i.e. trisomy of chromosome 21. Langdon Down reported it in 1866.
It is due to trisomy of 21st chromosome that the number is 47. Such condition of trisomy appears due to the formation of the n+1 male of female gamete subsequently fertilization by normal n gamete i.e. n+n+1.
Formation of n+1 gamete takes place due to the phenomenon of non-disjunction at anaphase stage of meiosis, where paired homologous chromosomes fail to separate.
This is found in higher age mothers with age 35 to 40 years.
This type of meiotic abnormality is not expected to run in families. But sometimes, ‘familial Down’s syndrome’ appears due to translocation of major part of chromosome 21 to chromosome 14. Such individuals are with 46 chromosomes with partial trisomy of chromosome 21.
The affected children have the broad forehead, short neck, flat hands with stubby fingers, open mouth, projecting lower lip with a long extending tongue and are mentally retarded. The child is mongoloid in appearance with slanting eyes and folds on the eyelid.
Klinefelter’s Syndrome is a set of symptoms obtain because of an extra copy of X- chromosome in the human male. Such persons have 47 chromosomes with one extra X-chromosome, i.e., 44+XXY.
This person is a man with some female characters like enlarged breasts (gynecomastia) one long limb, the degeneracy of seminiferous tubules, sparse body hairs, mental retardation, etc.
There may be the greater number of X chromosomes 44+XXXY ascertainable by 2 Barr bodies in interphase or 44+XXXXY etc.resulting in skeletal abnormalities, low mental ability, etc.
The addition of extra Y leads to 44+XYY (47) chromosomes. The males with such condition show above average height and subnormal intelligence. They are prone to psychopathic tendencies.
The presence of extra X chromosome in females with 44+XXX:44+XXXX etc. will show abnormal sexual developments and mental retardation. Females bear normal genitalia.
Turner’s syndrome is a common type of female genetic disorder characterized by hypogonadism. The incidence rate is 1 in 2500-3000 live female births. It was first discovered by H.H. Turner (1938).
Karyotypic studies showed that genotype of the female suffering from Turner’s syndrome is 45, X (44+XO) in which one X-chromosome is less than the normal karyotype. So the female is monosomic for sex chromosome.
The individual is a woman but is characterized by short stature little breasts, reduced ovaries and uterus, no oogenesis and menstrual cycle, little pubic hair mental retardation, infertility, webbing of the neck, peripheral lymphedema, heavy neck muscles, somatic cells with no sex chromatin, etc.
Turner’s syndrome originates from the development of an abnormal zygote formed by the fusion of an abnormal egg (with no X-chromosome) and a typical gymnosperm(sperm with X-chromosome) or due to the fusion of a normal egg,(with X-chromosome) and abnormal sperm(with no sex chromosome).
Phenylketonuria is autosomal recessive inborn error of metabolism that results in decreased metabolism of the amino acid phenylalanine.
It is characterized by the abnormal increase in the level of phenylalanine in the blood due to the absence of enzyme phenylalanine hydroxylase.
The Excess of phenylalanine changes into phenyl pyruvic acid which damages the brain and causes mental illness in the child. It is inherited as an autosomal recessive trait backwardness in the child.
Sickle cell anemia
Sickle cell anemia is caused by a gene(Hbs) which is lethal in homozygous condition, but it has a slight detectable effect in the heterozygous state.
In sickle cell anemia, a change in the shape of red blood cells occurs in the venous blood.These erythrocytes show a marked change in their structure attaining a sickle-shaped structure in being deficient in oxygen tension. As a result rupturing of the cell may take place and chronic hemolytic anemia is caused.
This disease caused when gene responsible for hemoglobin produced by the recessive alleles which differ in one amino acid. i.e., it replaces valine in place of glutamic acid.it incorporates valine in place of glutamic acid.
Techniques to detect fetal disorders during early pregnancy:
- Chorionic villi sampling (CVS)
- Noninvasive techniques
Amniocentesis is a test based on the chromosomal pattern in the amniotic fluid surrounding the developing embryo.
At the early stages of pregnancy, with the help of sonography technique, the location of the placenta is determined. Then a little amount of amniotic fluid is drawn out by passing a special surgical syringe needle into the abdominal wall and uterine wall into the amniotic sac containing amniotic fluid.
The amniotic fluid contains cells from fetus skin and respiratory tract. These cells are cultured, and then they are used to determine chromosomal abnormalities and metabolic disorders.
Unfortunately, amniocentesis technique is being misused to kill the healthy female fetuses. Amniocentesis is banned for the determination of sex to avoid female foeticide.
Misuse of Amniocentesis
The aim of this technique is to determine metabolic disorders in the fetus, genetically controlled congenital diseases, and sex of the developing baby. So amniocentesis is a prenatal diagnostic procedure.
Steps involved in this technique:-
- Sonography (using high-frequency ultrasound waves ) is used to determine the location of the fetus to prevent accidental damage to the fetus.
- Near about 14th and15th week after conception, a fine hollow needle is passed through the abdominal and uterine wall of a pregnant female into the amniotic cavity.
- A small amount of amniotic fluid is withdrawn. It contains fetal skin cells along with some proteins, especially enzymes. The cells can be cultured in vitro for further examination.
The drawn somatic cells of fetal skin with the amniotic fluid are stained to determine the presence of Barr body.
The Presence of Barr body in the cells indicates that the developing fetus in the female. Female is with 2 X-chromosomes out of which one X-chromosome is active, while another X-chromosome is inactive and heterochromatised into a darkly stained Barr body.
By doing karyotypic studies of the somatic cells, then abnormalities due to changes in chromosome number can be determined.
On performing, enzyme analysis of the amniotic fluid, many inborn metabolic disorders like alcaptonuria, phenylketonuria, etc. can be determined. These inborn errors occur due to inactivity of specific enzymes due to gene mutations or absence of that enzyme.
So with the help of amniocentesis technique, if it is confirmed that the child is likely to suffer from severe, congenital defect, the mother can go for abortion. Abortion or Medical termination of pregnancy (MTP) is intentional or voluntary termination of pregnancy before the fetus becomes viable. That is a most widely used method of fertility control in the world. MTP is comparatively safe up to 12 weeks (first trimester) of pregnancy.
However, many times the amniocentesis is being misused. Mothers even get their healthy fetus aborted if it is a female. This is just equivalent to the killing of a healthy child.
Chorionic villi sampling (CVS)
In chorionic villi sampling (CVS) technique the doctor inserts a narrow, flexible tube through mother’s vagina into the uterus and then withdraws a little amount of fetal tissue (chorionic villi) from the placenta.
Non-invasive technique – Ultrasound imaging
One of the widely used noninvasive methods to determine fetal condition is ultrasound imaging. Another technique is based on the fact that a few fetal blood cell leaks across the placenta of them into the mother’s bloodstream. The blood sample from the mother provides enough fetal cells to test for genetic disorders.
Foetoscopy is another technique in which a thin tube needle containing a viewing scope is inserted into the uterus of the female, a direct view of fetus to the physician