Common and Rare Birth Defects or Congenital Disorders and Their Causes

Congenital disorders are abnormalities of structure or function that are present at birth, including those that do not become manifest until later in life.

Here are some of the commonest and rarest birth defects and their usual causes.

Tay-Sachs disease

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Fundus photograph showing retina changes associated with Tay-Sachs disease.

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Tay-Sachs disease or TSD is a genetic disorder that is fatal in its most common variant known as Infantile Tay-Sachs disease. Victims of Tay-Sachs disease deteriorate physically and mentally from about 6 months of life until death at about 6 years because an enzyme needed to break down a specific fatty substance is nonfunctional. This disease is especially common in the nervous tissue of the brain. This type of single gene disorder is inherited, one from each parent, to cause the disease.

Galactosemia

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Galactosemia results from an inability to metabolize the sugar galactose, a constituent of milk. Its incidence is about 1 per 47,000 births (classic type). It is much rarer in Japan and much more common in Italy, specifically the traveler region. Galactosemia is also very common within the Irish traveler population. This is attributed to consanguinity within a relatively small gene pool. It is inherited and has no cure but you can take steps to prevent or minimize galactosemia symptoms and complications. The treatment is the strict avoidance of all sources of galactose. The most common source is lactose, which is the milk sugar that breaks down to galactose and glucose.

Phenylketonuria

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(Blood is taken from a two-week old infant to test for phenylketonuria)

Phynylketonuria results from an inability to convert one amino acid; phynylalanine, to another, tyrosine. Left untreated, this condition can cause problems with brain development, leading to progressive mental retardation and seizures. However, PKU is one of the few genetic diseases that can be controlled by diet. A diet low in phenylalanine and high in tyrosine can be a very effective treatment. There is no cure. Damage done is irreversible so early detection is crucial. This disease is also inherited.

Muscle Disorder Myotonic Dystrophy

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The presence of one copy of a mutant gene is sufficient to cause serious disease. Myotonic dystrophy (MD) is a chronic, slowly progressing, highly variable inherited multisystemic disease that can manifest at any age from birth to old age. It is characterized by wasting of the muscles, posterior subcapsular iridescent cataracts, heart conduction defects, endocrine changes and myotonia (difficulty relaxing a muscle).

Down’s syndrome

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Down syndrome, Down’s syndrome, or trisomy 21 is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. Three copies of chromosome 21 rather than two. The condition is characterized by a combination of major and minor differences in structure. Often Down syndrome is associated with some impairment of cognitive ability and physical growth as well as facial appearance. Down syndrome in a baby can be identified with amniocentesis during pregnancy or at birth.

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(Example of white spots on the iris known as Brushfield spots)

Individuals with Down syndrome may have the physical characteristic of white spots on the iris known as Brushfield spots.

Congenital Cerebral Palsy

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Some causes of congenital cerebral palsy are multiple births, infections, exposure to methylmercury and others. Cerebral palsy (CP) is an umbrella term encompassing a group of non-progressive, non-contagious conditions that cause physical disability in human development. This defect is caused by damage to the motor control centers of the young developing brain and can occur during pregnancy (about 75 percent), during childbirth (about 5 percent) or after birth (about 15 percent) up to about age three. In a study, the incidence in six countries surveyed was 2.12-2.45 per 1000 live births.

Congenital Heart Defects

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One cause of this defect is by mothers who are diabetic. A congenital heart defect (CHD) is a defect in the structure of the heart and great vessels of a newborn. Most heart defects either obstruct blood flow in the heart or vessels near it or cause blood to flow through the heart in an abnormal pattern, although other defects affecting heart rhythm can also occur. Heart defects are among the most common birth defects and are the leading cause of birth defect-related deaths.

Sickle-cell Disease

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This disease is inherited. Sickle-cell disease or sickle-cell anemia is a blood disorder characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells’ flexibility and results in their restricted movement through blood vessels, depriving downstream tissues of oxygen. The disease is chronic and lifelong: individuals are most often well, but their lives are punctuated by periodic painful attacks and a risk of various other complications. Life expectancy is shortened, with older studies reporting an average life expectancy of 42 and 48 years for males and females, respectively.

Congenital Hypothyroidism

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The most common cause of this defect is iodine deficiency. CHT is a condition of thyroid hormone deficiency present at birth. Approximately 1 in 4000 newborn infants has a severe deficiency of thyroid function, while even more have mild or partial degrees. If untreated for several months after birth, severe congenital hypothyroidism can lead to growth failure and permanent mental retardation. Treatment consists of a daily dose of thyroid hormone by mouth.

Huntington’s Chorea

This disorder is inherited and caused by the length of a repeated section of a gene exceeding the normal range. Huntington’s disease, also called Huntington’s chorea, chorea major, or HD, is a genetic neurological disorder characterized after onset by uncoordinated, jerky body movements called chorea and a decline in some mental abilities, which can lead to affected aspects of behavior. As the disorder progresses, these symptoms cause complications that reduce life expectancy.

Cystic Fibrosis

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(Aspergillus fumigatus - A common fungus which can lead to worsening lung disease in people with CF)

Cystic fibrosis (also known as MF, mucovoidosis, or mucoviscidosis) is a hereditary disease affecting the exocrine (mucus) glands of the lungs, liver, pancreas, and intestines, causing progressive disability due to multi-system failure.

Fetal Alcohol Syndrome

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This congenital defect is brought about by liquor drinking by the mother. Fetal alcohol syndrome (FAS) is a disorder of permanent birth defects that occurs in the offspring of women who drink alcohol during pregnancy. Although prenatal alcohol exposure does not automatically result in FAS, the current recommendation is not to drink at all during pregnancy.

Cleft Lip and Palate

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Cleft lip (cheiloschisis) and cleft palate (palatoschisis), which can also occur together as cleft lip and palate are variations of a type of clefting congenital deformity caused by abnormal facial development during gestattion. This type of deformity is sometimes referred to as a cleft. A cleft is a sub-division in the body’s natural structure, regularly formed before birth. A cleft lip or palate can be successfully treated with surgery soon afterbirth. Cleft lips or palates occur in somewhere between one in 600-800 births.

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