Cartilage Hair Hypoplasia (CHH) is also known as metaphyseal dysplasia, McKusick type. The disorder was recognized as a clinical entity in 1965, when Victor McKusick and colleagues described the condition in an inbred Amish population (1). The term “metaphyseal” relates to the metaphysis, which is the wide region located at the ends of long bones. The name “Cartilage Hair Hypoplasia” was coined due to the characteristic features: fine, sparse hair and cartilage abnormalities.
This dysplasia is caused by a mutation of the gene encoding the RNA component of the ribonuclease mitochondrial RNA processing complex (RMRP). The locus of the RMRP gene is on chromosome 9p13. The mutation affects cartilage development.
Cartilage Hair Hypoplasia is a relatively rare congenital disorder. It is most prevalent among the Old-world Amish and Finnish populations. Among Amish people, the incidence is approximately 1.5 in 1000 live births, whereas in Finland, it is 1 in 18,000 to 23,000 (2).
The physical characteristics of Cartilage Hair Hypoplasia include a short limbed form of disproportionate short stature with fine, sparse hair. Intelligence is typically average.
Face and Skull:
- Relatively average face and skull
- Fine, sparse, and light hair
- Sparse eyebrows and eyelashes
Trunk, Chest and Spine:
- Anterolateral chest deformity
- Prominent sternum
- Moderately flared lower rib cage
What Are the X-Ray Characteristics?
The major radiographic features in infancy include shortened long tubular bones. The femur is curved with rounded distal epiphyses. Anterior angulation of the sternum and short ribs are also characteristic. The radiographic features in children and adults include short, flared, and irregularly sclerotic metaphyses of tubular bones.
Deformities are more prominent in the knee region than in the proximal femur. A postero-lateral subluxation of the radial head is observed in some patients. The fibula is disproportionately long, most notably at the distal end.
There is minimal craniocaudal widening of interpediculate distance in lumbar spine. Small sagittal and coronal diameters of the vertebrae are typical. Flaring and cupping at the costochondral junction of ribs is also characteristic. The metacarpals and phalanges are severely affected.
In infancy, diagnosis of Cartilage Hair Hypoplasia is difficult; not until 9 to 12 months of age do the abnormalities become apparent. Radiographic examination provides the greatest insight. Widened metaphyses, short long bones, elongated fibulae, and anterior angulation of the sternum are all indicative of Cartilage Hair Hypoplasia. Hair hypoplasia is only a positive criterion; the absence of hair hypoplasia does not warrant the exclusion of Cartilage Hair Hypoplasia as a possible diagnosis.
Scoliosis is typical of Cartilage Hair Hypoplasia. Depending on the degree of curvature, it can be managed observation, bracing, or surgery.
Intestinal malabsorption occurs in approximately 10% of patients. The intestinal malabsorption problem tends to improve on its own.
Hirschsprung Disease occurs in approximately 10% of patients. Surgical intervention is oftentimes necessary. Postoperative mortality rates are nearly 40%, due to severe enterocolitis-related septicemia and a compromised immune system.
Humoral immunity is typically compromised. Nearly 56% of younger children experience recurrent infections, especially respiratory tract infections. Children are unusually susceptible to chicken pox. In McKusick’s original study, 6 patients died due to fatal varicella pneumonia. Currently, Acyclovir is most often prescribed to treat the varicella. Patients have a predisposition to cancer, especially non-Hodgkin’s lymphoma and basal cell carcinoma. Again, this susceptibility is due to the compromised T-cell immunity.
Anemia can occur in varying degrees in childhood. In anemic patients, decreased red blood cell proliferation is also observed. Most anemic patients recover spontaneously by adulthood; however fatal hypoplastic anemia can occur in infants. The prevalence of anaemia seems to correlate to the severity of the immunodeficiency and the degree of growth failure.
It is vital to keep a close watch for the possibility of serious infection or malignancy. Varicella and other live virus vaccinations should not be given if the diagnosis is established.
- McKusick, V. A.; Eldridge, R.; Hostetler, J. A.; Egeland, J. A.; Ruangwit, U. Dwarfism in the Amish. II. Cartilage-hair hypoplasia. Bull. Johns Hopkins Hosp. 116: 285-326, 1965.
- Mäkitie, Outi. Cartilage-Hair Hypoplasia: Clinic radiological and genetic study of an inherited skeletal dysplasia. University of Helsinki, Finland. 1992.
From Nemours' KidsHealth
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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.
Here are some facts that other people may not realize about dwarfism and those who have it.
- 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 is called achondroplasia.
- can and most often does happen 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.
- 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, drive cars, 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.
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 happen in any pregnancy. If parents have some form of dwarfism themselves, the odds are likely 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 dysplasia, which are conditions of abnormal bone growth. They're divided into two types: short-trunk and short-limb dwarfism. People with short-trunk dwarfism have a shortened trunk with more average-sized limbs, whereas those with short-limb dwarfism have an average-sized trunk but shortened arms and legs.
By far, the most common skeletal dysplasia is achondroplasia, a short-limb dwarfism that happens 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 happens 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. Along with achondroplasia and diastrophic dysplasia, it is one of the more common types of dwarfism. In one type of SED, the lack of growth in the trunk area may not become apparent until the child is school age; other forms are apparent at birth. Kids with this disorder also might have clubfeet, cleft palate, and vision and/or hearing issues.
In general, dwarfism caused by skeletal dysplasias results in what is known as disproportionate short stature — meaning the limbs and the trunk are not of the same proportion 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.
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 baby's appearance, growth pattern, 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 increase a child's growth, but skeletal dysplasias cannot be "cured."
People with skeletal dysplasias 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 have hydrocephalus (excess fluid around the brain). They may also have a greater risk of developing apnea (a temporary stop in breathing during sleep). This can be due to abnormally small bone anatomy or 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 also may become apparent, including:
- development of some motor skills, such as sitting up and walking happening at older ages than an average-sized child
- 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
Not every type of dwarfism has all of these problems associated with it, and proper medical care can help with many of them. Surgery also can be used to improve some of the leg, hip, and spine problems people with dwarfism sometimes face.
Nonsurgical options can help, too — for instance, excessive weight can worsen many orthopedic problems, so a dietitian 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 general tips to keep in mind:
- Treat your child according to his or her age and developmental level, and not size. For example, a 2-year-old should not still be using a bottle, even if he or she is the size of a 1-year-old. And, 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 and a well-placed step stool 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 outwardly 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 and, importantly, that his or her dwarfism doesn't cause you any anger. It also helps 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 thing, 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: September 05, 2017