Genetic Causes of Intellectual Disabilities: Cri du Chat Syndrome and Cornelia De Lange Syndrome (CdLS)
Cri du Chat syndrome
Like Cockayne syndrome, the Cri du Chat syndrome is caused by an irregularity on chromosome 5. This rare disorder results from a genetic defect on the short arm of this chromosome. The deletion of this genetic material interferes with the body's ability to grow cells. It is unknown whether the disorder is genetic or random. Cri du Chat is very rare. Its estimated occurrence is between 1 in 20,000-50,000.
Physical symptoms of Cri du Chat syndrome include an unusually small head and small jaw. Eyes are spaced far apart with a downward slant. Ears tend to be low-set and malformed. Extra skin is found in front of the ears. The fingers and toes may be joined (webbed). Physical features are apparent at birth. Birth weight is low and rate of growth is slow.
The feature most associated with Cri-du-Chat syndrome is a cat-like cry in infancy. The cry is readily recognized by most physicians. The unique high-pitched mewing fades as the baby grows.
Cornelia De Lange syndrome (CdLS)
The Cornelia De Lange syndrome (CdLS) was discovered twice. Cornelia De Lange, was a Dutch professor of pediatrics. She identified the mental and physical characteristics of De Lange syndrome in 1933. However, the syndrome had been previously described by another physician named Brachman in 1916. That earlier account was recorded in a book that became damaged and was not widely accessible. Today, De Lange syndrome is also known as Brachman-De Lange syndrome in recognition of Dr. Brachman's original discovery.
Researchers have linked CdLS to the Nipped B-like (NIBL) gene on chromosome 5. The NIBL gene affects embryonic development. The NIBL gene activates other genes via a protein it creates. Therefore, problems with NIBL cause a domino effect for genetic development. About half of the individuals diagnosed with Cornelia De Lange syndrome have a mutated NIBL gene. Presently, researchers are trying to determine if there are other genes involved in the disorder besides NIBL.
Physical characteristics include low-set ears and bushy eyebrows. The hairline is unusually low. Eyelashes tend to be extraordinarily long. The bridge of the nose is depressed and the tip of the nose points upward. The nostrils face forward. The mouth has an unusual 'carp-shape' and the teeth are small and spaced widely apart. The upper jaw tends to protrude.
Children with Cornelia De Lange syndrome have smaller heads than average. Their hands are flat and shaped like a spade. Fingers tend to be short. There is a deep crease running across the palm of the hand. They are short in stature and have excessive hair on their bodies.
People with this syndrome grow at a slower rate than average. Development is delayed. Medical problems associated with the syndrome include heart defects, hearing loss, poor eyesight, and abnormal skeletal structure and development.
The actual rate of occurrence of CdLS is unknown. It is estimated it occurs in 1 in 10,000 to 30,000 births. The condition might be inherited. Siblings of children with CdLS have a 2% to 5% chance of having the genetic disorder as well.