What Percent of Babies Are Born With Birth Defects

Every year, about 7.9 million infants (6% of worldwide births) are born with serious nascency defects. With the causes of over 50% of birth defects unknown, how do we diagnose and prevent them?

Every year, an estimated 7.9 million infants (6% of worldwide births) are born with serious birth defects. Although some congenital defects can be controlled and treated, an estimated 3.2 million of these children are disabled for life. Moreover, nascency defects are the leading cause of infant mortality in the United States. Simply where do these defects come up from? Although some nascence defects are inherited, others are a production of harmful environmental factors known as teratogens, and still others are multifactorial, resulting from a complex interaction of genetic and ecology influences. However, in approximately one-half of all nativity defect cases, the causes are unknown (Christianson et al., 2006).

Genetic causes of birth defects fall into iii full general categories: chromosomal abnormalities, single-gene defects, and multifactorial influences. Prenatal surround tin can play a major office in the evolution of defects in all three categories, especially those linked to multifactorial causes.

Chromosomal Abnormalities

A person's genetic makeup is determined at conception. It is then, during the nuclear events of fertilization, that the genetic causes of many birth defects are adamant. For example, chromosomal abnormalities, or big-scale duplications or deletions of chromosomal segments or entire chromosomes, can become apparent during this flow. Many zygotes that bear such abnormalities exercise not develop into embryos, but among those that are carried to term, trisomy 21 (Downwardly syndrome), trisomy 13 (Patau syndrome), and trisomy 18 (Edwards syndrome) are the most frequent birth defects. Embryos with these 3 conditions will develop severe disabilities regardless of the ecology factors associated with the pregnancy.

Unlike Down syndrome patients, who usually have a relatively long life span, children with Patau and Edwards syndromes often die soon after birth (March of Dimes, 2006). Individuals diagnosed with Patau syndrome suffer from neurological problems, mental and motor deficiencies, and polydactyly (Figure 1), also as middle, centre, and spine defects (Patau et al., 1960). Those built-in with Edwards syndrome endure mental retardation, breathing and feeding difficulties, delayed growth, and malformations of the kidneys, intestines, and heart (Edwards et al ., 1960; Van Dyke & Allen, 1990). Thankfully, both of these devastating syndromes are rare.

Effigy 2: Primary Down syndrome is caused by the presence of three copies of chromosome 21.

(a) A child who has Down syndrome. (b) Idiogram of a person who has principal Down's syndrome.

(a) © 2006 iStock.com/JSCook. (b) National Institutes of Health.

Downwardly syndrome, on the other manus, is by far the nearly mutual chromosomal abnormality, affecting one in 800 babies. The take chances of having a child with this status increases with maternal historic period, ascension exponentially after a adult female reaches age 35. For example, in young mothers, the frequency of trisomy 21 is virtually 1 in 2,000, but this frequency rises to ane in 100 when a woman is twoscore and to 1 in 12 when she is l years old (Figure 2). People who accept Downwardly syndrome suffer from moderate to severe mental retardation and a broad variety of health problems, including heart defects, leukemia, and Alzheimer's affliction. The severity of these defects varies widely, however, and the majority of people with Down syndrome live semi-contained lives, with an average life expectancy of 56 in the United States (Eyman et al., 1991). Aneuploidies such as Down syndrome can generally be detected by the presence of boosted chromosomes or chromosome translocations in a karyotype or FISH profile.

Single-Gene Defects

As opposed to chromosomal abnormalities, single-cistron defects are usually inherited. For example, phenylketonuria (PKU) is a heritable status caused past the malfunction of the PAH enzyme that breaks down the amino acid phenylalanine. Because this enzyme is coded for by the PAH factor on chromosome 12, PKU falls nether the category of unmarried-gene defects.

Interestingly, many single-cistron defects are variably prevalent amidst different racial and indigenous groups. For instance, sickle-jail cell anemia (a disorder of the hemoglobin) is most common among people of African, Indian, and Mediterranean descent, whereas Tay-Sachs and Sandhoff diseases (both of which touch on the nervous organization) occur almost frequently amid Ashkenazi Jews. Tay-Sachs and Sandhoff diseases are both caused by a lack of the protein hexosaminidase, which controls the levels of fatty buildup in the brain. Specifically, autosomal recessive mutations in the HEXA factor on chromosome 15 cause various forms of Tay-Sachs, while the presence of a mutated HEXB gene on chromosome five causes Sandhoff. These disorders mainly affect young children, who typically die during the first few years of life from progressive neural degeneration.

Multifactorial Influences

In certain cases, a combination of genetic mutations and teratogens leads to the development of multifactorial birth defects. Although the exact causes of most multifactorial disorders are poorly understood, doctors can often identify common trends amongst like weather condition. Folate deficiency, for example, appears to play a role in various malformations of the neural tube, but the cumulative causes of such malformations and their relative contribution are rather complex. Neural tube defects take also been linked to trisomy xviii, numerous mutations in the genes necessary for the evolution of the nervous system, and exposure to sure epilepsy drugs. Of the different forms of neural tube defects, a condition known equally anencephaly is arguably the most severe. Anencephalic babies lack most of their brain and are often stillborn or dice soon afterward nascency. Spina bifida is a (relatively) less severe defect of the neural tube characterized by a series of deformities that are associated with incomplete enclosure of the spinal cord by the twenty-eighth day of development. The exposed spinal cord and the surrounding tissues are usually sealed surgically before long later on birth, but the neurological effects, including partial paralysis and loss of float control, oftentimes concluding a lifetime.

Of course, not all nativity defects accept such profound consequences. Consider, for example, cleft lip and palate; this is a multifactorial birth defect that, if left uncorrected, tin can create difficulties with eating and speech. Children born with cleft lip ordinarily undergo corrective surgery at an early age. Although genes definitely play a part in the development of this defect, ecology factors, including smoking and the use of antiseizure drugs, have been associated with a greater gamble of bearing a child with cleft lip and/or palate (Ericson et al., 1979; Knight & Rhind, 1975).

Prenatal Surround

Information technology is hard to overemphasize the importance of prenatal environment to a developing fetus. Indeed, a significant mother's health, diet, and level of exposure to toxins and environmental pollutants all take a straight effect on fetal development. For example, one of the most highly publicized cases of widespread toxin exposure associated with a pronounced increase in birth defects involves the use of Agent Orange, an herbicide that contains the poison dioxin, by the U.S. Army during the Vietnam War. Since the finish of that conflict, the frequency of birth defects in those areas exposed to dioxin has risen to near three times the norm. Dioxin, a production of industrial processes, disrupts the function of nuclear receptors and interferes with cell signaling. Moreover, dioxin is fat soluble and takes a long fourth dimension to degrade, which means it can build up over fourth dimension in soil, in water, and in the fatty tissue of animals that humans consume.

Other environmental toxins that might impairment a fetus are taken voluntarily, such as drugs, booze, and cigarettes. For instance, excessive maternal alcohol consumption often causes fetal alcohol syndrome, which is characterized by defects of major organs, abnormal facial features, and mental retardation. Similarly, smoking during pregnancy has been linked to an increased risk of stillbirths, low nativity weights, and cleft lip and/or palate (Ericson et al., 1979; Knight & Rhind, 1975). Although studies have not demonstrated a stiff correlative link between a high incidence of birth defects and consumption of moderate amounts of alcohol and tobacco, doctors strongly recommend complete abstinence from smoking and drinking during pregnancy.

Yet another major factor linked to abnormal prenatal development is poor diet during pregnancy. Certain foods, such as seafood with high mercury content, should be consumed in moderation, whereas other high-vitamin foods are encouraged. Dietary supplements, such every bit folate (vitamin B9) and iodine taken before and during the early stages of pregnancy, tin can aid in evolution of the neural tube. It is important to empathize, all the same, that skilful diet and a healthy lifestyle do not ensure a healthy child, although they do play a protective office in sure individuals.

Limiting the Frequency of Nascence Defects

Although some congenital defects cannot be prevented, improvements in health intendance, nutrition, and pedagogy tin can reduce their frequency and phenotypic severity. The increasing use of prenatal genetic screens and preimplantation genetic diagnosis (PGD) is also helping limit the frequency and the severity of nascence defects. These advances are a cracking tool, only they as well have a surprising downside. Specifically, deleterious genetic mutations that have a recessive design of inheritance will remain in the population if the parents seeking PGD are allowed to select only healthy embryos to exist carried to term. The current utilise of this technique, however, is limited to the select few who tin beget information technology, and so this phenomenon will not have a noticeable bear on on the overall population for quite some time.

References and Recommended Reading

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Christianson, A., et al. March of Dimes Global Report of Birth Defects: The Subconscious Cost of Dying and Disabled Children. (2006) (accessed August 28, 2008).

Edwards, J. H., et al. A new trisomic syndrome. Lancet 1, 787–790 (1960)

Ericson, A., et al. Cigarette smoking as an etiologic factor in cleft lip and palate. American Journal of Obstetrics and Gynecology 135, 348–351 (1979)

Eyman, R. K., et al. Life expectancy of persons with Down syndrome. American Journal of Mental Retardation 95, 603–612 (1991)

Knight, A. H., & Rhind, E. G. Epilepsy and pregnancy: A study of 153 pregnancies in 59 patients. Epilepsia xvi, 99–110 (1979)

Korkko, J., et al. Widely distributed mutations in the COL2A1 gene produce achondrogenesis blazon Two/hypochondrogenesis. American Journal of Medical Genetics 92, 95–100 (2000)

March of Dimes. Chromosomal abnormalities. (2006) (accessed Aug. 28, 2008)

Patau, G., et al. Multiple built anomaly caused past an extra autosome. Lancet i, 790–793 (1960)

Van Dyke, D. C., & Allen, M. Clinical management considerations in long-term survivors with trisomy 18. Pediatrics 85, 753–759 (1990).

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Source: http://www.nature.com/scitable/topicpage/birth-defects-causes-and-statistics-863

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