Diastrophic Dysplasia

The term "diastrophic" is Greek and means "crooked". Although diastrophic dysplasia occurs in most countries, the highest prevalence is found in Finland (1 in 33,000) where the carrier rate in the population is 1 – 2% (3). The incidence in non-Finnish populations is considerably lower, being 1 in 500,000 live births (6).

 
How Diastrophic Dysplasia Is Inherited

Diastrophic dysplasia is inherited as an autosomal recessive trait, with very wide variability of phenotypic expression. Approximately 5% of cases constitute new mutations (6).

 
Causes of Diastrophic Dysplasia

Diastrophic dysplasia is caused by a mutation in the gene coding for a sulfate transporter protein that is essential for normal cartilage function. This protein is called DTDST and was first identified by Hastabacka and colleagues in 1994 (1). The gene is located on chromosome 5 (5q31-q34). Mutations in the same gene are responsible for lethal chondrodysplasias.

Proteoglycans are complex molecules that absorb water and facilitate load bearing in articular cartilage. Reduction in sulfate transporter concentrations in chondrocytes causes under-sulfation of the proteoglycan matrix and predisposes individuals to early degenerative joint disease. Diastrophic dysplasia affects chondrocyte function in the growth plate, epiphyseal region and other areas such as the trachea.

 
Physical Characteristics

The physical characteristics of diastrophic dysplasia include a short limbed form of disproportionate short stature. Both joint dislocations and joint contractures can be present. Intelligence is typically average.

Face & Skull
  • Narrow nasal bridge and broad midportion of the nose
  • Long and broad philtrum
  • High, broad forehead
  • Square jaw
  • Cleft palate in approximately 50% of children
  • Capillary hemangiomas called an "Angel's kiss" can be present in the midforehead region. They will disappear or fade with time.
  • In the majority of patients in first 2 weeks of life, cystic swellings of the ear appear but resolve spontaneously, resulting in the characteristic “cauliflower ear” deformity.
Trunk, Chest, & Spine:
Arms & Legs:
  • Shortening of limbs
  • "Hitchhiker’s thumb." Due to poor development of the bone supporting the thumb, the main thumb joint deviates outwards
  • Limited movement of the fingers due to symphalangism
  • Dislocations of the elbow and shoulder
  • Dislocated kneecap
  • Clubfoot
  • Abnormal gait
  • Weight bearing on balls of feet and toes with compensatory knee and hip flexion
What are the X-ray characteristics?

The radiographic features of Diastrophic Dysplasia include short and broad long bones of the limbs. The metaphyses are flared and crescent-shaped, and flattened epiphyses are typical. The epiphyses of the proximal tibias are triangular and larger than those of the distal femoral epiphyses. The metacarpals, metatarsals, and phalanges are deformed and shortened. Cervical kyphosis and thoraco-lumbar kyphoscholiosis are characteristic at different ages. There is a moderate narrowing of the interpediculate distances within the lower lumbar segments of spine. The hips are either partially or completely dislocated.

 
Making the Diagnosis

The condition is typically recognized at birth based on physical and radiographic evaluation. Milder variants or atypical cases may not be diagnosed until a later age. If suspicions arise during a prenatal ultrasound, molecular testing can be done from an aminocentesis sample.

In parents who already have children with diastrophic dysplasia, an ultrasound scan or molecular genetic testing (using DNA from amniocentesis or chorionic villus sampling) in the first trimester of pregnancy offers the possibility of prenatal diagnosis of this condition.

 
Musculoskeletal Problems
Cervical Spine

Cervical kyphosis is present in 30 – 50% of individuals. It is due to hypoplasia of the vertebral bodies and progressive degenerative changes in the intervertebral joints. Kyphosis can be sufficiently severe and will cause a predisposition to spinal cord compression and quadriplegia (weakness of all 4 extremities and incontinence). Short, sharply angulated curves are associated with severe kyphosis and increase the incidence of neurological abnormalities. Surgery may be necessary to alleviate the spinal cord compression in the neck. A halo and vest device is usually employed after surgery to support the neck until stable fusion is achieved. Occasionally, the kyphosis will resolve spontaneously.

Thoracolumbar Spine

Scoliosis, although not apparent at birth, will become severe as weight bearing increases. The curves usually develop around 5 years of age but can develop even before walking age. The spine curvature causes trunk deformity and barrel chest. Three distinct patterns of scoliosis occur: early progressive, idiopathic-type and mild non-progressive. Kyphoscoliosis occurs frequently (up to 90% of patients) in the lumbar region of the spine. Lumbar lordosis is increased due to exaggerated thoracic kyphosis and concomitant hip flexion contractures (hip joint is fixed with the thigh bent forwards).

Severe Clubfoot

Severe clubfoot is almost always present and typically requires surgical release. Surgery is usually undertaken around 1-year of age, to enable the child to start walking. In spite of early intervention, recurrence of the foot deformity is common and an osteotomy may become necessary. Special shoes are oftentimes required.

Progressive Sublixation

Progressive subluxation of the hips occurs because the soft articular cartilage is unable to perform its normal function of load bearing. Superimposed joint contractures around the hips and knees lead to restricted movement and deformity. If the deformity interferes with walking, an osteotomy is performed around the hips or knees. Due to the intrinsic cartilage abnormality, degenerative joint disease (arthritis) is common. Flexion deformities are pronounced. Knees are dislocated. Hip or knee replacement surgery is usually necessary in early to mid-adult life and typically has successful results.

 
Problems Elsewhere in the Body
Respiratory Obstruction

Respiratory obstruction, including laryngeal stenosis, may occur in newborns. The mortality rate due to respiratory distress can approach 25% in early infancy.

Hypoplastic Cartilage

Hypoplastic cartilage in the trachea and larynx causes voice abnormalities and breathing difficulty.

Small Auditory Canals

Small auditory canals are characteristic, but this does not usually impair hearing. However, deformity of the middle ear ossicles can result in
hearing loss.

 
What to Look For

In infancy, it is important to be regularly monitored by a pediatric orthopedic surgeon so that future problems of the feet and spine can be managed and possibly evaded. Surgery is usually performed before walking age to correct foot deformities.

Later in life, patients must look out for worsening foot deformities, progressive curvature of the spine, and hip pain in early adult life (due to arthritis). Common surgical procedures intended to correct these problems include an osteotomy of the foot or lower leg (to achieve a plantigrade foot) or hip replacement surgery (for progressive degenerative arthritis).

Occasionally, spinal cord compression in the neck can lead to quadriparesis, resulting in a loss of limb function. Symptoms to watch for include a loss of walking or reduced endurance, altered sensations in the arms and legs, or incontinence. Oftentimes patients undergo spinal fusion surgery in the neck or lower back, along with decompression of the spinal cord.

Generally all skeletal dysplasias warrant multidisciplinary attention. Regular assessment by an orthopedist, geneticist, pediatrician, dentist, neurologist, and physical therapist will provide the most comprehensive treatment.

 
References
  1. Hastbacka, J.; Sistonen, P.; Kaitila, I.; Weiffenbach, B.; Kidd, K. K.; de la Chapelle, A. : A linkage map spanning the locus for diastrophic dysplasia (DTD). Genomics 11: 968-973, 1991.
  2. Jones, Kenneth L. Recognizable Patterns of Human Malformation. Philadelphia, PA: Elsevier Saunders. 2006.
  3. Poussa, Mikko. Merikanto, Juhani. Ryoppy, Soini. Marttinen, Eino. Kaitila, Ilkka. The Spine in Diastrophic Dysplasia. Spine; 16(8):881-887. 1991.
  4. Scott, Charles I. Dwarfism. Clinical Symposium, 1988; 40(1):9-10.
  5. Spranger, Jurgen W. Brill, Paula W. Poznanski, Andrew. Bone Dysplasias: An Atlas of Genetic Disorder of Skeletal Development. Oxford: Oxford University Press. 2002.
  6. Diastrophic Dysplasia Booklet http://pixelscapes.com/ddhelp/DD-booklet/

Trusted Insights from Nemours' KidsHealth

Dwarfism

There's been a lot of discussion over the years about the proper way to refer to someone with dwarfism. Many people who have the condition prefer the term "little person" or "person of short stature." For some, "dwarf" is acceptable. For most, "midget" definitely is not.

But here's an idea everyone can agree on: Why not simply call a person with dwarfism by his or her name?

Being of short stature is only one of the characteristics that make a little person who he or she is. If you're the parent or loved one of a little person, you know this to be true.

But here are some facts that other people may not realize about dwarfism and those who have it.

Dwarfism:

  • is characterized by short stature. Technically, that means an adult height of 4 feet 10 inches or under, according to the advocacy group Little People of America (LPA).
  • can be caused by any one of more than 300 conditions, most of which are genetic. The most common type, accounting for 70% of all cases of short stature, is called achondroplasia.
  • can and most often does occur in families where both parents are of average height. In fact, 4 out of 5 of children with achondroplasia are born to average-size parents.

Dwarfism isn't:

  • an intellectual disability. A person who has dwarfism is typically of normal intelligence.
  • a disease that requires a "cure." Most people with one of these conditions live long, fulfilling lives.
  • a reason to assume someone is incapable. Little people go to school, go to work, marry, and raise children, just like their average-size peers.

What Causes Short Stature?

More than 300 well-described conditions are known to cause short stature in a child. Most are caused by a spontaneous genetic change (mutation) in the egg or sperm cells prior to conception. Others are caused by genetic changes inherited from one or both parents.

Similarly, depending on the type of condition causing the short stature, it is possible for two average-size parents to have a child with short stature, and is also possible for parents who are little people to have an average-size child.

What prompts a gene to mutate is not yet clearly understood. The change is seemingly random and unpreventable, and can occur in any pregnancy. If parents have some form of dwarfism themselves, the odds are much greater that their children will also be little people. A genetic counselor can help determine the likelihood of passing on the condition in these cases.

Dwarfism has other causes, including metabolic or hormonal disorders in infancy or childhood. Chromosomal abnormalities, pituitary gland disorders (which influence growth and metabolism), absorptive problems (when the body can't absorb nutrients adequately), and kidney disease can all lead to short stature if a child fails to grow at a normal rate.

Types of Short Stature

Most types of dwarfism are known as skeletal dysplasias, which are conditions of abnormal bone growth. They're divided into two types: short-trunk and short-limb dysplasias. People with short-trunk dysplasia have a shortened trunk with more average-sized limbs, whereas those with short-limb dysplasia have an average-sized trunk but shortened arms and legs.

By far, the most common skeletal dysplasia is achondroplasia, a short-limb dysplasia that occurs in about 1 of every 15,000 to 40,000 babies born of all races and ethnicities. It can be caused by a spontaneous mutation in a gene called FGFR3, or a child can inherit a change in this gene from a parent who also has achondroplasia.

People with achondroplasia have a relatively long trunk and shortened upper parts of their arms and legs. They may share other features as well, such as a larger head with a prominent forehead, a flattened bridge of the nose, shortened hands and fingers, and reduced muscle tone. The average adult height for someone with achondroplasia is a little over 4 feet.

Diastrophic dysplasia is a different form of short-limb dwarfism. It occurs in about 1 in 100,000 births, and is also sometimes associated with cleft palate, clubfeet, and ears with a cauliflower-like appearance. People who have this diagnosis tend to have shortened forearms and calves (this is known as mesomelic shortening).

Spondyloepiphyseal dysplasias (SED) refers to a group of various short-trunk skeletal conditions that occurs in about 1 in 95,000 babies. Along with achondroplasia and diastrophic dysplasia, it is one of the most common forms of dwarfism. In some forms, a lack of growth in the trunk area may not become apparent until the child is between 5 and 10 years old; other forms are apparent at birth. Kids with this disorder also might have clubfeet, cleft palate, and a barrel-chested appearance.

In general, dwarfism caused by skeletal dysplasias results in what is known as disproportionate short stature — meaning the limbs and the trunk are not the same proportionally as those of typically-statured people.

Metabolic or hormonal disorders typically cause proportionate dwarfism, meaning a person's arms, legs, and trunk are all shortened but remain in proportion to overall body size.

Diagnosis

Some types of dwarfism can be identified through prenatal testing if a doctor suspects a particular condition and tests for it.

But most cases are not identified until after the child is born. In those instances, the doctor makes a diagnosis based on the child's appearance, failure to grow, and X-rays of the bones. Depending on the type of dwarfism the child has, diagnosis often can be made almost immediately after birth.

Once a diagnosis is made, there is no "treatment" for most of the conditions that lead to short stature. Hormonal or metabolic problems may be treated with hormone injections or special diets to spark a child's growth, but skeletal dysplasias cannot be "cured."

People with these types of dwarfism can, however, get medical care for some of the health complications associated with their short stature.

Some forms of dwarfism also involve issues in other body systems — such as vision or hearing — and require careful monitoring.

Possible Complications and Treatments

Short stature is the one quality all people with dwarfism have in common. After that, each of the many conditions that cause dwarfism has its own set of characteristics and possible complications.

Fortunately, many of these complications are treatable, so that people of short stature can lead healthy, active lives.

For example, a small percentage of babies with achondroplasia may experience hydrocephalus (excess fluid around the brain). They may also have a greater risk of developing apnea — a temporary stop in breathing during sleep — because of abnormally small or misshapen anatomy or, more likely, because of airway obstruction by the adenoids or the tonsils. Occasionally, a part of the brain or spinal cord is compressed. With close monitoring by doctors, however, these potentially serious problems can be detected early and surgically corrected.

As a child with dwarfism grows, other issues may also become apparent, including:

  • delayed development of some motor skills, such as sitting up and walking
  • a greater susceptibility to ear infections and hearing loss
  • breathing problems caused by small chests
  • weight problems
  • curvature of the spine (scoliosis, kyphosis, and/or lordosis)
  • bowed legs
  • trouble with joint flexibility and early arthritis
  • lower back pain or leg numbness
  • crowding of teeth in the jaw

Proper medical care can alleviate many of these problems. For example, surgery often can bring relief from the pain of joints that wear out under the stress of bearing weight differently with limited flexibility.

Surgery also can be used to improve some of the leg, hip, and spine problems people with short stature sometimes face.

Nonsurgical options may help, too — for instance, excessive weight can worsen many orthopedic problems, so a nutritionist might help develop a healthy plan for shedding extra pounds. And doctors or physical therapists can recommend ways to increase physical activity without putting extra stress on the bones and joints.

Helping Your Child

Although types of dwarfism, and their severity and complications, vary from person to person, in general a child's life span is not affected by dwarfism. Although the Americans with Disabilities Act protects the rights of people with dwarfism, many members of the short-statured community don't feel that they have a disability.

You can help your child with dwarfism lead the best life possible by building his or her sense of independence and self-esteem right from the start.

Here are some tips to keep in mind:

  • Treat your child according to his or her age, not size. If you expect a 6-year-old to clean up his or her room, don't make an exception simply because your child is small.
  • Adapt to your child's limitations. Something as simple as a light switch extender can give a short-statured child a sense of independence around the house.
  • Present your child's condition — both to your child and to others — as a difference rather than a hindrance. Your attitude and expectations can have a significant influence on your child's self-esteem.
  • Learn to deal with people's reactions, whether it's simple curiosity or outright ignorance, without anger. Address questions or comments as directly as possible, then take a moment to point out something special about your child. If your child is with you, this approach shows that you notice all the other qualities that make him or her unique. It will also help prepare your child for dealing with these situations when you're not there.
  • If your child is teased at school, don't overlook it. Talk to teachers and administrators to make sure your child is getting the support he or she needs.
  • Encourage your child to find a hobby or activity to enjoy. If sports aren't going to be your child's forte, then maybe music, art, computers, writing, or photography will be.
  • Finally, get involved with support associations like the Little People of America. Getting to know other people with dwarfism — both as peers and mentors — can show your child just how much he or she can achieve.

Reviewed by: Angela L. Duker, MS, CGC
Date reviewed: March 2011