Common Genetic Conditions
The graph above shows the incidence of common genetic conditions. Some like the Trisomies are more common with advancing maternal age whilst the others or not affected by maternal age.
Pregnancies at increased risk of common genetics conditions such as Trisomy 21 (Down Syndrome, Trisomy 18 (Edward Syndrome) , Trisomy 13 (Patau Syndrome), sex chromosome aneuploidy such as Turner Syndrome, Klinefelter Syndrome and Jacob Syndrome and microdeletions such as 22q11.2 deletion syndrome, Prader-Willi syndrome, Angelman syndrome, Cri-du-chat syndrome and those with Triploidy can be identified by the Panorama NIPT blood test. Pregnant women then have the option of prenatal diagnostic tests such as amniocentesis or CVS or newborn testing to confirm or exclude the condition. Pregnancies in which the pregnant woman or her partner are carriers of an autosomal recessive condition such as cystic fibrosis can be identified by Horizon or Invitae carrier screening. If both parents are carriers of a particular condition there would be a 1 in 4 chance of having a baby with that condition and then they would have the option of prenatal diagnostic tests such as amniocentesis or CVS or newborn testing to confirm or exclude the condition.
Trisomy 21 (Down syndrome)
Babies with Down syndrome have copies of chromosome 21 and have intellectual disabilities that range from mild to severe. Children with Down syndrome will need extra medical care depending on the child’s specific health problems. Early intervention has allowed many individuals with Down syndrome to lead healthy and productive lives. The presence of medical conditions, like heart defects, can affect the lifespan in these children and adults; however, most individuals with Down syndrome will live into their 60s. Miscarriage occurs in about 30% of pregnancies with Down syndrome while overall about 1 in 700 babies are born with Down syndrome.
Trisomy 18 (Edwards syndrome)
Babies with trisomy 18 have three copies of chromosome 18 and have severe intellectual disabilities and birth defects typically involving the heart, brain, and kidneys. Babies with trisomy 18 can also have visible birth defects such as an opening in the lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate), a small head, clubbed feet, underdeveloped fingers, and toes, and a small jaw. Unfortunately, most pregnancies with trisomy 18 will miscarry. If born alive, most affected babies with trisomy 18 will pass away within the first few weeks of life. About 10 percent survive to their first birthday. Trisomy 18 occurs in approximately 1 in 3,000 live births.
Trisomy 13 (Patau syndrome)
Babies with trisomy 13 have three copies of chromosome 13 and have severe intellectual disabilities. They often have birth defects involving the heart, brain, and kidneys. Visible abnormalities include extra fingers and/or toes or an opening in the lip, with or without an opening in the palate. Given the severe disabilities, most pregnancies affected by trisomy 13 will miscarry. If born alive, most affected babies with trisomy 13 will pass away within the first few weeks of life. About 10 percent survive to their first birthday. Trisomy 13 occurs in approximately 1 in 5,000 live births.
Babies with triploidy have a complete extra set of chromosomes for a total of 69 chromosomes instead of the usual 46. At 10 weeks gestation, one in 1,000 pregnancies is affected by triploidy. It is extremely rare for these pregnancies to reach term as they typically spontaneously miscarry early in pregnancy. Those few liveborns usually pass away within days of delivery due to heart, brain, and kidney problems. Babies with triploidy also often have birth defects affecting the extremities and face.
Carrying a baby with triploidy can increase a mother’s risk for a variety of conditions: pre-eclampsia (which can lead to seizures) and excessive bleeding after delivery. In rare instances, triploid pregnancies can persist and progress to a type of cancer called choriocarcinoma. Knowing about triploidy allows the physician to monitor the health of the mother appropriately
Sex Chromosome Aneuploidy
Monosomy X (Turner syndrome)
Babies with monosomy X are females who have one X chromosome instead of two. Unfortunately, a high proportion of pregnancies with monosomy X will result in a miscarriage in the first or second trimester of pregnancy. Babies with monosomy X that make it to term may have heart defects, learning difficulties, and infertility. In most cases, girls with monosomy X will need extra medical care including hormone therapy at various stages of life.
XXY Syndrome (Klinefelter Syndrome)
Babies with XXY syndrome have two X chromosomes and one Y chromosome (XXY). This condition can be associated with learning difficulties and behavioral problems. People with Klinefelter syndrome might be infertile. About 1 in 1,000 babies will be born with Klinefelter syndrome.
Triple X syndrome
Babies with Triple X syndrome have three X chromosomes (XXX). Children with this condition could be taller than average and might experience learning difficulties or behavioural problems. Approximately 1 in 1,600 babies will be born with three X chromosomes.
XYY Syndrome (Jacob’s Syndrome)
Babies with XYY syndrome have one X chromosome and two Y chromosomes (XYY). Most babies with XYY syndrome do not have any birth defects. Children with XYY could be taller than average and have an increased chance for learning, speech, and behavioural problems. Approximately 1 in 1,300 babies will be born with one X chromosome and two Y chromosomes.
22q11.2 deletion syndrome
22q11.2 deletion syndrome, also called DiGeorge syndrome or Velo-Cardio-Facial syndrome (VCFS), is caused by a missing piece of chromosome number 22. About one in every 2,000 babies is born with 22q11.2 deletion syndrome. The majority of children with this disorder have heart defects, immune system problems, and specific facial features. Most children with 22q.11.2 deletion syndrome have mild-to-moderate intellectual disability and speech delays; some will also have low calcium levels, kidney problems, feeding problems, and/or seizures. About one in five children with 22q11.2 deletion syndrome have autism spectrum disorder; 1 in 4 adults with 22q11.2 deletion syndrome have a psychiatric illness, like schizophrenia.
Prader-Willi syndrome occurs when either a small piece of chromosome 15 is missing or when both copies of chromosome 15 come from the same parent (called uniparental disomy, or UPD). Babies with Prader-Willi syndrome have low muscle tone and problems with growth and feeding. Children with Prader-Willi syndrome have delayed milestones, short stature, rapid weight gain leading to obesity, and intellectual disability. About 1 in 10,000 babies are born with Prader-Willi syndrome.
Angelman syndrome happens when either a small piece of chromosome 15 is missing, or when both copies of chromosome 15 come from the same parent (called uniparental disomy, or UPD). About 1 in 12,000 babies are born with Angelman syndrome. Babies and children with Angelman syndrome have severe intellectual disability, delayed milestones, seizures, and problems with balance and walking.
1p36 deletion syndrome
1p36 deletion syndrome, also referred to as Monosomy 1p36 syndrome is caused by a missing piece of chromosome 1. Children with 1p36 deletion syndrome have intellectual disabilities. Most have heart defects and weak muscle tone. About half of affected individuals have seizures (epilepsy), behavioural problems, and hearing loss. Some children with 1p36 deletion syndrome also have vision problems or additional birth defects of other organs. About 1 in 5,000 newborn babies has 1p36 deletion syndrome.
A missing piece of chromosome 5 causes Cri-du-chat syndrome, also called 5p- (5p minus) syndrome. The name “Cri-du-chat” was given to this syndrome due to the high-pitched, cat-like cry that babies with this syndrome often make. Babies with Cri-du-chat syndrome typically have low birth weight, a small head size, and weak muscle tone. Feeding and breathing problems are common in infancy. Children with this disorder have moderate-to-severe intellectual disability, including speech and language delays. They may also have growth delays, behavior problems, and some have curvature of the spine (scoliosis). About one in every 20,000 babies is born with Cri-du-chat syndrome. They may also have heart defects, growth delay, behaviour problems and some have curvature of the spine.