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What is CCD?

Cleidocranial dysplasia (CCD) is a skeletal disorder characterized by open fontanelles (soft spot), small or absent clavicles (collarbones), and multiple dental abnormalities. It is a genetic birth defect caused by mutations to the RUNX2 gene. It occurs one in every one million births. It can be passed from an affected parent or can be a random mutation. Manifestations may vary among individuals in the same family.

Physical Characteristics

HEIGHT

Short stature:  Average height for men is 5’2”-5’6”. Average height for women is 4”9”-4’10”

HEAD and NECK

Delayed closure of fontanelles (soft spots)

Large, open soft spot at birth that may close or remain open throughout life

Parietal bossing (broad/flat forehead)

FACE

Small mid-face: the portion of the face comprising nasal (nose), maxillary (upper jaw), and zygomatic bones (cheekbones) and the soft tissues covering these bones

Frontal bossing:  prominent, protruding forehead

Metric groove:  vertical dent in the middle of the forehead, normally not present at birth

Micrognathia:  small lower jaw

EARS

Deafness

EYES

Hypertelorism:  increased distance between the eyes

NOSE

Low nasal bridge

MOUTH

Narrow, high-arched palate (roof of mouth)

TEETH

Failure to lose baby teeth

Failure for permanent teeth to come in on their own

Supernumerary (extra) teeth

Retention cysts

Enamel hypoplasia: thin enamel caused by poor enamel formation

Crowded teeth

Jaw malocclusion: poor bite

RESPIRATORY

Respiratory distress in early infancy

CHEST

Narrow thorax (chest)

Ability to touch shoulders together

Small scapula

Small or absent clavicles (collarbones) with sloping shoulders

Short ribs

Cervical ribs: extra ribs that arise from vertebrae in the neck

SKELETAL

Osteopenia: reduced bone mass

Increased bone fragility

SKULL

Wormian bones: extra bone pieces that occur within the joints of the cranium

Bossing (protruberance) of frontal bone

Bossing of occipital bone

Bossing of parietal bone

Calvarial (skull) thickening

Absent or small frontal sinuses

Absent or small paranasal sinuses

Large foramen magnum: the hole at the base of the skull through which the spinal cord passes

SPINE

Spondylolysis:  a defect in the vertebral arch in the lumbar or cervical vertebrae

Spondylolisthesis:  a condition where one vertebral body is slipped forward over another

Scoliosis:  a lateral curve in the spine

Kyphosis: a curve in the spine that results in a bulge at the upper back

PELVIS

Wide pubic symphysis (the joint in the pubic bone)

Delayed mineralization of pubic bone

Broad head of the femur bone

Short neck of the femur bone

Coxa vara:  hip deformity where the head and shaft of the femur is reduced to less than 120 degrees, resulting in a short leg and a limp

Underdeveloped iliac wing (pelvic bone)

HANDS

Brachydactyly: short fingers

Long second metacarpal (hand bone)

Short middle bones of second and fifth fingers

Cone-shaped finger tips

Short and broad thumbs

LEGS

Gene valgum:  a condition in which knees are deviated towards midline of the body and touch one another when the legs are straightened (“knock knee”)

FEET

Lower or flattened arches in the feet

NEUROLOGIC

Syringomyelia:  fluid-filled cysts in the spinal cord

What are other medical conditions seen in individuals with CCD?

recurrent sinus infections

upper-airway complications

recurrent ear infections

high incidence of cesarean section

mild degree of motor delay in children under age five years.

Fine-motor skills (grasping a pencil, using a spoon)
Gross-motor skills (walking, hopping, climbing stairs)

How is CCD Diagnosed?

1) Physical exam and clinical findings.

CCD can be diagnosed by they “characteristic triad” of

small or absent clavicles,  open fontanelles (soft spot), and supernumerary (extra) teeth

Other clinical findings include small mid-face, abnormal teeth, hand abnormalities, normal intellect

2) X-ray findings:

Skull: wide or open fontanels (soft spot), presence of wormian bones; delayed bone formation; poor development of paranasal, frontal or mastoid sinuses; crowded or extra teeth

Chest:  narrow thorax, small or absent clavicles, small scapulae

Pelvis:  wide symphysis pubis, small pelvic bones, wide sacroiliac joint, short femoral neck

Hands:  long second metacarpal, underdeveloped distal finger bones, cone-shaped finger tips

3) Genetic testing. The test looks for changes in the RUNX2 gene. The gene is found 60-70% of the time in people with a clinical diagnosis of CCD.

Prenatal diagnosis can be made by ultrasound examination in offspring of affected parent as early as 14 weeks.

Other conditions that share characteristics with CCD:

Congenital psyeduoarthrosis of the clavicle

Pyknodysostosis

Crane-Heist syndrom

Manibuloacral dysplasia

Yunis-Varon syndrome

Hypophosphatasia

CDAGS syndrome

Parietal foramina with cleidocranial dysplasia

Children with CCD should be monitored for the following:

Orthopedic complications

Dental abnormalities

Upper-airway obstruction

Hearing loss

Osteoporosis

What causes CCD?

Humans have 23 pairs of chromosomes. 22 pairs are called autosomes the 23rd pair, the sex chromosomes, differ between males and females.
Humans have about 20,000 functioning (or protein coding) genes, found on the 23 chromosomes.
Humans have two of each gene, one from mother and one from father. If your parents each give you matching genes, they are called homozygous. If the genes are different from each other, they are called heterozygous.
A mutation is the changing of the structure of a gene.
When one gene has less or no function, it is called a loss-of function mutation.
The gene causing CCD is the RUNX2 gene and is found on the 6th chromosome.
The 6th chromosome has 1,048 protein coding genes, the RUNX2 gene is one of these.

Cleidocranial dysplasia (CCD) is caused by heterozygous loss-of-function mutation in the RUNX2 gene on the 6th chromosome.
The mutation to the one gene can be: 1) passed from an affected parent 2) can be a new or random mutation.
CCD is an autosomal dominant trait. This means the gene affected is on an autosome (one of the 22 pairs of chromosomes that is not the sex chromosome). It only takes a single abnormal gene (not an abnormal chromosome) from either parent to cause an autosomal disorder.A dominant trait means an abnormal gene from one parent can cause the disease. This happens when the matching gene from the other parent is normal. The abnormal gene dominates. A parent with an autosomal dominant conditions has a 50% chance of having a child with the condition. This is true for each pregnancy (Each pregnancy is a 50/50 chance. The child’s risk for the disease does not depend on whether their sibling has the disease).

CHILDREN WHO DO NOT INHERIT THE ABNORMAL GENE WILL NOT DEVELOP THE DISORDER.
CHILDREN WHO DO NOT INHERIT THE ABNORMAL GENE CANNOT PASS ON THE DISORDER.

Timeline & Evolution of CCD

The main clinical features of CCD include persistently open fontanels (soft spots) with bulging skull, underdeveloped or absent of the clavicles (collarbones), wide pubic symphysis (the joint of the pubic bones), short middle phalanx (bone) of the fifth fingers, dental anomalies, and often vertebral (bones of the spinal column) abnormalities.

Link to article: Cleidocranial dysplasia: clinical and molecular genetics by Stefan Mundlos
www.ncbi.nlm.nih.gov/pmc/articles/PMC1734317/pdf/v036p00177.pdf

The evolution of Cleidocrainal dysplasia knowledge/research

TIMELINE

1765 Reports of the defect first appeared
1898 Marie and Sainton Coined dysostose cleidocranienne hereditaire or cleidocranial dysostosis
1909 Skeleton of a 25 year-old man showed underdeveloped clavicles, open anterior soft spot, and touching knees (genu valgum).
1951 Jackson 356 descendants were traced to the Chinese man Arnold, 70 of whom were affected with the “Arnold Head.” He lived in South Africa and had 7 wives.
1976 Arvystas Reported a family with delayed eruption of baby and permanent teeth, probably CCD
1987 Dore et al Described association of CCD and syringomyelia (fluid-filled cysts in the spinal cord)
1987 Silence, et al Proposed the gene symbol “CCD”

Studied CCD in mice and found the homozygous (2 mutated RUNX2 genes) state in mice was lethal.

1990 Jensen Height and radius length are decreased, especially in females. CCD is a generalized skeletal dysplasia.
1992 Chitayat et al Described the range of variability in affected members in 3 generations of family
1993 Reed and Houston Concluded that under formation of the hyoid bone could be added to the delayed process of bone formation that affects the skull, teeth, pelvis, and extremities.
1993 Nienhaus et al Proposed that CCD gene is located on chromosome 6.
1995 Mundlos et al The CCD gene was assigned to chromosome 6 ( 6p21)
2001 Cooper et al Found the following complications that had previously been unrecognized: genu valga (knock-knee), scoliosis, pes planus (flat foot), sinus infections, upper respiratory complications, recurrent middle ear infections and hearing loss.  Primary rate of c-sections was increased. Dental abnormalities: extra teeth, failure to lose baby teeth, abnormal jaw alignment.
2002 Morava et al Mutation causes abnormalities due to defective mineralization.
2002 Unger et al Osteopenia, osteoporosis and decreased alkaline phosphatase likely occur in a minority of patients with CCD.
2005 Zheng et al Humans with CCD have altered endochondral bone formation (where process where bones grow in length, where cartilage turns to bone)
2005 Baumert et al Sequenced the RUNX2 gene and identified 12 RUNX2 mutations. They observed mild to full-blown expression of the CCD characteristics, with variability in families.
2010 El-Gharbawy et al RUNX2 appears to play a role in the formation of bone and bone cell differentiation.
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