Birth Defects PDF

# Birth Defects - About 3 to 4 percent of babies are born with some type of birth defect (affecting 1 in every 33 babies born in the US). - Birth defects are also referred to as “congenital anomalies” or “congenital abnormalities.” - They may affect appearance, organ function, and physical and me...

# Birth Defects - About 3 to 4 percent of babies are born with some type of birth defect (affecting 1 in every 33 babies born in the US). - Birth defects are also referred to as “congenital anomalies” or “congenital abnormalities.” - They may affect appearance, organ function, and physical and mental development. - Terms used to describe the study of these disorders are teratology (Gr. teratos; monster) and dysmorphology. - Teratogens – factors or agents that cause birth defects - Most birth defects are present within the first three months of pregnancy, when the organs are still forming - It can be very mild or severe – some birth defects are life-threatening, in which case a baby may only live for a few months - An estimated 303,000 newborns die within 4 weeks of birth every year, worldwide, due to birth defects ## What Causes Birth Defects? - Birth defects can be a result of: - genetics - lifestyle choices and behaviors - exposure to certain medications and chemicals - infections during pregnancy - a combination of these factors - However, the exact causes of certain birth defects are often unknown. ## What Are The Risk Factors For Birth Defects? - All pregnant women have some risk of delivering a child with a birth defect - Risk increases under any of the following conditions: - family history of birth defects or other genetic disorders - drug use, alcohol consumption, or smoking during pregnancy - maternal age of 35 years or older - inadequate prenatal care - untreated viral or bacterial infections, including sexually transmitted infections - use of certain high-risk medications, such as isotretinoin and lithium - women with pre-existing medical conditions, such as diabetes ## Teratogens Associated With Human Malformations | Teratogen | Congenital Malformations | |---|--------------------------------| | **Infectious agents** | | | Rubella virus | Cataracts, glaucoma, heart defects, deafness, tooth abnormalities | | Cytomegalovirus | Microcephaly, blindness, mental retardation, fetal death | | Herpes simplex virus | Microphthalmia, microcephaly, retinal dysplasia | | Varicella virus | Limb hypoplasia, mental retardation, muscle atrophy | | HIV | Microcephaly, growth retardation | | Toxoplasmosis | Hydrocephalus, cerebral calcifications, microphthalmia | | Syphilis | Mental retardation, deafness | | **Physical agents** | | | X-rays | Microcephaly, spina bifida, cleft palate, limb defects | | Hyperthermia | Anencephaly, spina bifida, mental retardation, facial defects, cardiac abnormalities, omphalocele, limb defects | | **Chemical agents** | | | Cocaine | Growth retardation, microcephaly, behavioral abnormalities, gastroschisis | | Alcohol | Fetal alcohol syndrome, short palpebral fissures, maxillary hypoplasia, heart defects, mental retardation | | Thalidomide | Limb defects, heart malformations | | Aminopterin | Anencephaly, hydrocephaly, cleft lip and palate | ## Common Birth Defects - **Structural defects** are when a specific body part is missing or malformed. The most common structural defects are: - Heart defects - Cleft lip or palate - Spina bifida - Clubfoot - **Functional or developmental birth defects** cause a body part or system not to work properly. These often cause disabilities of intelligence or development. The most common types of functional or developmental birth defects include: - Down syndrome - Sickle cell disease ## How Are Birth Defects Diagnosed? - Prenatal ultrasounds are used to diagnose certain birth defects in utero - More in-depth screening options, such as blood tests and amniocentesis, may also be done. These tests are usually offered to women who have higher-risk pregnancies due to family history, advanced maternal age, or other known factors - Prenatal tests can help determine whether the mother has an infection or other condition that’s harmful to the baby - A physical examination and hearing test – used to diagnose birth defects after the baby is born - Blood test called the newborn screen used to diagnose some birth defects shortly after birth, before symptoms occur ## Prevention of Birth Defects - Many birth defects can be prevented - Supplementation of salt or water supplied with iodine eliminates mental retardation and bone deformities resulting from cretinism - Placing women with diabetes or Phenylketonuria under strict metabolic control prior to conception reduces the incidence of birth defects - Folate supplementation lowers the incidence of neural tube defects (spina bifida, anencephaly), and also reduces the risk for hyperthermia-induced abnormalities - Avoidance of alcohol and other drugs during all stages of pregnancy reduces the incidence of birth defects - It is important for physicians prescribing drugs to women of childbearing age to consider the possibility of pregnancy and the potential teratogenicity of the compounds - Recently, hundreds of children have been born with severe craniofacial, cardiac, and neural tube defects produced by retinoids (used for the treatment of cystic acne, common acne and reducing wrinkles) ## Down Syndrome (Trisomy 21) - Down syndrome is a condition in which a person has an extra chromosome – chromosome 21 - A medical term for having an extra copy of a chromosome is “trisomy” – Trisomy 21 - This extra copy changes baby’s body and brain development, which can cause both mental and physical challenges. - The incidence of Down syndrome is approximately one in 2,000 conceptuses for women under age 25. This risk increases with maternal age to one in 300 at age 35 and one in 100 at age 40 - People with Down syndrome usually have growth retardation, varying degrees of mental retardation, craniofacial abnormalities. - Have relatively high incidences of leukemia, infections, thyroid dysfunction, and premature aging - Nearly all develop signs of Alzheimer’s disease after age 35 ## Down Syndrome - Some common physical features of Down syndrome include: - A flattened face, especially the bridge of the nose - Almond-shaped eyes that slant up - A short neck - Small ears - A tongue that tends to stick out of the mouth - Tiny white spots on the iris (colored part) of the eye - Small hands and feet - A single line across the palm of the hand (palmar crease) - Small pinky fingers that sometimes curve toward the thumb - Poor muscle tone or loose joints - Shorter in height as children and adults ## Types of Down Syndrome - There are three types of Down syndrome. - **Trisomy 21:** About 95% of people with Down syndrome have Trisomy 21 - Each cell in the body has 3 separate copies of chromosome 21 instead of the usual 2 copies - **Translocation Down syndrome:** - Affects about 3% of the people with Down syndrome. - Extra part or a whole extra chromosome 21 is present, but it is attached or “trans-located” to a different chromosome (13, 14 or 15) rather than being a separate chromosome 21 - **Mosaic Down syndrome:** Affects about 2% of the people with Down syndrome. - Some cells have 3 copies of chromosome 21, but other cells have the typical two copies of chromosome 21. - These children may have the same features as other children with Down syndrome. However, they may have fewer features of the condition due to the presence of some (or many) cells with a typical number of chromosomes. ## Trisomy 18 and Trisomy 13 - **TRISOMY 18:** Patients show the following features: - Mental retardation, congenital heart defects, low-set ears, and flexion of fingers and hands - Deficient mandible (micrognathia), renal anomalies, syndactyly (2 or more digits are fused together), and malformations of the skeletal system. - The incidence of this condition is one in 5,000 newborns. - 85% are lost between 10 weeks of gestation and term, whereas those born alive usually die by 2 months of age. - **TRISOMY 13:** Patients show the following features: - Mental retardation, holoprosencephaly (brain doesn’t properly divide into the right and left hemispheres), congenital heart defects, deafness, cleft lip and palate, and eye defects, such as microphthalmia, anophthalmia, and coloboma - The incidence of this abnormality is one in 20,000 live births, and more than 90% of the infants die in the first month after birth. ## Klinefelter syndrome - Genetic condition that results when a boy is born with an extra copy of the X chromosome. - Genetic condition affecting males, and it often isn't diagnosed until adulthood. - The incidence is approximately one in 500 males. - May adversely affect testicular growth, resulting in smaller than normal testicles, which can lead to lower production of testosterone. - Syndrome may also cause reduced muscle mass, reduced body and facial hair, and enlarged breast tissue. - Most men with Klinefelter syndrome produce little or no sperm. ## Turner syndrome (Monosomy X) - A condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing - Occurs in approximately one out of every 2,000 female live births. - Are characterized by the absence of ovaries (gonadal dysgenesis) and short stature. - Other common associated abnormalities are webbed neck, lymphedema (swelling due to lymphatic obstruction) of the extremities, skeletal deformities, low set ears and a broad chest with widely spaced nipples. ## Birth defects due to structural abnormalities of chromosomes - Involve one or more chromosomes, usually result from chromosome breakage. - Breaks are caused by environmental factors, such as viruses, radiation, and drugs - **Cri-du-chat syndrome:** - Caused by partial deletion of the short arm of chromosome 5 - Affected children have a cat-like cry, microcephaly, mental retardation, and congenital heart disease - Microdeletions of few genes of a chromosomes also results in birth defects - Microdeletion of few genes on the long arm of chromosome 15 result in Angelman and Prader-Willi syndromes - **Angelman syndrome:** - Microdeletion occurs in maternal chromosome 15 - Children are mentally retarded, cannot speak, exhibit poor motor development, and are prone to unprovoked and prolonged periods of laughter - **Prader-Willi syndrome:** - Microdeletion occurs in paternal chromosome 15 - Affected individuals are characterized by hypotonia, obesity, mental retardation, hypogonadism, and cryptorchidism - **Miller-Dieker syndrome:** - Microdeletion of few genes on short arm of chromosome 17 of both parents - Affected individuals will have developmental delay, seizures, and cardiac and facial abnormalities ## Neural Tube Defects (NTD) - Neural Tube Defects occur when the neural tube does not close properly. - The neural tube forms the brain and spinal cord. - These types of birth defects develop very early during pregnancy, often before a woman knows she is pregnant. - The two most common NTDs are spina bifida (a spinal cord defect) and anencephaly (a brain defect). ## Spina Bifida - It is a type of neural tube defect (NTD). - Spina bifida can happen anywhere along the spine if the neural tube does not close all the way. - When the neural tube doesn’t close all the way, the backbone that protects the spinal cord doesn’t form and close as it should. This often results in damage to the spinal cord and nerves. - Spina bifida might cause physical and intellectual disabilities that range from mild to severe. - The severity depends on: - The size and location of the opening in the spine. - Whether part of the spinal cord and nerves are affected. ## Spina Bifida - types - **Myelomeningocele** - Most serious type of spina bifida. - With this condition, a sac of fluid comes through an opening in the baby’s back. - Part of the spinal cord and nerves are in this sac and are damaged. - This type of spina bifida causes moderate to severe disabilities - loss of feeling in the person’s legs or feet, and not being able to move the legs - **Meningocele** - A sac of fluid comes through an opening in the baby’s back. - But, the spinal cord is not in this sac. - There is usually little or no nerve damage. - Cause minor disabilities - **Spina Bifida Occulta** - Mildest type of spina bifida – “hidden” spina bifida. - There is a small gap in the spine, but no opening or sac on the back. - Spinal cord and the nerves usually are normal. - Many times, spina bifida occulta is not discovered until late childhood or adulthood. - Usually does not cause any disabilities. ## Anencephaly - Anencephaly is a serious birth defect in which a baby is born without parts of the brain and skull. - Anencephaly happens if the cranial part of the neural tube does not close all the way. - This often results in a baby being born without the front part of the brain (forebrain). - The remaining parts of the brain are often not covered by bone or skin. - Almost all babies born with anencephaly will die shortly after birth. - It occurs in about 3 of 10,000 pregnancies in the U.S. each year.