Morquio Syndrome

Morquio Syndrome is another name for mucopolysaccharidosis IV (MPS IV); it was first described by Luis Morquio in 1919 (4). The frequency of Morquio syndrome is 1 in 640,000 births (7).

 
How Morquio Syndrome Is Inherited

Morquio syndrome follows an autosomal recessive inheritance pattern (9).

 
Causes of Morquio Syndrome

A mutation is the GALNS gene, which encodes for N-acetyl galactosamine-6-sulfatase, causes Morquio, type A (4). Type B is caused by mutations of the GLB1 gene, which encodes for β-galactosidase (4). Both enzymes, however, are responsible for keratan sulfate degradation. In type A, the activity of the sulfatase was found to be less than 1% (6). Due to the enzymes’ ineffectiveness, mucopolysaccharides aggregate within intracellular lysosomes. Mucopolysaccharides are long, unbranched chains of repeating saccharide, or sugar, units. They are important components of the body’s connective tissues and are often times covalently linked to proteins. In Morquio Syndrome, the lysosomal enzymes that are responsible for breaking down mucopolysaccharides are ineffective. As a result, the long sugar molecules begin to collect in the body’s cells and connective tissues. The accumulation ultimately causes cellular damage that manifests as skeletal malformations.

 
Physical Characteristics
Face & Skull
  • Mildly coarse facial features
  • Accentuated lower portion of the face
  • Broad mouth
  • Short anteverted nose
  • Corneas of the eyes become cloudy
  • Widely spaced teeth
  • Hypoplasia of tooth enamel
Trunk, Chest, & Spine:
  • Barrel shaped chest
  • Flaring lower rib cage
  • Prominent sternum
  • Stunted neck and trunk
  • Considerably short spine marked platyspondyly
  • Abnormal posture
Arms & Legs:
  • Severe flexion deformities of the limbs
  • Ligamentous laxity, especially at the wrists and small joints
  • Joint restriction prominent at the larger joints, most notably at the hips
  • Awkward gait
  • Knock-knees
  • Flat feet
  • Prominent buttocks
  • Short and stubby hands
What are the X-ray characteristics?

The major radiographic features of Morquio syndrome include marked platyspondyly in the thoracic and lumbar spine. The shape of the vertebrae change from ovoid, to ovoid with anterior projection, to flat. 

Odontoid hypoplasia with atlanto-axial instability is typical. With progression of the disease, acute thoracolumbar kyphosis is possible; the first indication of spinal cord compression is at the level of C1/C2.The skull is mildly dolichocephalic with underdevelopment of mastoid cells and flat or concave mandibular condyles. A flaring lower rib cage with pectus carinatum is typical of the thorax. 

A premature fusion of the ossification centers of the sternum usually occurs. The long bones are short and curved, with irregular tabulation. Metaphyses are irreguarly wide. Ossification centers tend to develop slowly. Coxa valga is characteristic, along with an abnormal femoral neck and flattening of the femoral head. 

Genu Valgus and a medial spur of tibial metaphysis are often times seen. The bases of the second through fifth metacarpals are conically shaped. The feet have irregular contour with delayed ossification of the tarsal bones. There is central constriction and general shortness of the metacarpals and phalanges.

 
Making the Diagnosis

Morquio Syndrome is typically not recognized at birth. Onset does not occur until the second to fourth year of life. The most frequently recognized symptoms include gait disturbance and growth deficiency.

Diagnostic procedures include flexion-hyperextension radiographs of the cervical spine and/or MRI of the cervical or thoracolumbar spine.

To confirm the diagnosis, two-dimension electrophoresis or thin-layer chromatography of isolated urinary glycosaminoglycans is employed.

Heterozygote detection is possible.

Prenatal recognition can be done using amniotic fluid cells and chorionic villi.

 
Musculoskeletal Problems
Lower Limbs

Pectus carinatum and knock-knee deformity (genu valgus) begin at approximately 3 years of age, and progressively worsen as growth continues. Ligamentous laxity plays a part in the development of knock-knee. In severe cases, the knock-knee may interfere with ambulation. Around age 7 or 8, a patient typically has a lower limb osteotomy to correct the deformity. Typically, the outcome is good, and the results are permanent because growth typically stops around this age. However, due to the habitual atlantoaxial instability, neurological integrity may be compromised, and patients have considerable difficulty in learning to walk again.

Hips

Dislocation of the hips is typically observed, especially as weight-bearing increases. The dislocation, however, is asymptomatic and usually does not impair function. Therefore, most patients abstain from surgical intervention. Yet if patients are considerably physically active, especially as adults, symptomatic osteoarthritis of the hip may develop.

Upper Limbs

Ligamentous laxity is severe, especially of the wrists and ankles. The force able to be delivered by the long flexors of the fingers and thumbs becomes considerably weak. The wrists need to be stabilized, which will help to increase the effectiveness of the muscles and to improve function. Wrist fusions have been attempted, however most attempts have failed.

Spine

Atlanto-axial instability along with myelopathy of the upper cervical spinal cord is a severe problem. Upper motor neurons begin to lose function, there is vague pain in the lower limbs, superficial paresthesias of the feet, vibratory sensation progressively worsens, mobility becomes impaired, and the ability to control the sphincters and to breathe is compromised. If left untreated, most males lose their ability to walk and may possibly die of chronic respiratory failure. The course is typically not as severe in female patients. The rate of progression of cervical myelopathy is variable, however surgical intervention is needed to halt the downward trend. Fusion of the upper cervical spine is frequently recommended. However, care must be taken when administering the anesthesia, due to the risks associated with atlanto-axial instability. Spinal fusion may be supplemented by instrumentation (metal implants) to support the bones until the fusion mass consolidates. In cases of diagnostic doubt, further information can be obtained by means of an MRI scan (with flexion-extension views and CSF flow studies). It allows accurate determination of the degree of spinal cord compression and space available for the cord.

 
Problems Elsewhere in the Body
Respiratory

By late teens and adulthood, the ribs are nearly horizontal and the sagittal diameter of the chest is greater than average. As a result, respiratory expansion becomes considerably impaired. Moreover, frequent upper respiratory tract infections, including otitis media, may occur due to the malformation of the rib cage. The trachea is narrow and may collapse during head flexion. Lung function tests and sleep studies are frequently used to diagnose breathing problems in skeletal dysplasias. Regular review by a pulmonologist is recommended. Prolonged breathing difficulties may warrant a tracheostomy and long-term ventilatory support.

Cardiac

Cardiac complications may occur, including cardiomyopathy, valvular disease, or a late onset of aortic regurgitation. Cardiac anomalies are predominately left sided. Severe cases have resulted in death before the age of 20.

Ear

Hearing loss, inguinal hernia, and hepatomegaly are all problems associated with the ear. Hearing aids and tubes are often times required.

Eye

Corneal opacity is typical once patients reach age 5; glaucoma of the eyes and pigmentary retinal degeneration may occur in older patients. Ophthalmologic examination is needed at frequent intervals.

Skin

Cutaneous abnormalities may also be present, including loose, thickened, tough, and inelastic skin, particularly of the extremities. Generalized telangiectasia of the face and limbs has also been reported.

Teeth

Appropriate dental care is required due to the hypoplasia of tooth enamel. Teeth often brown and discolor easily. The permanent posterior teeth have pointed cusps; there is often times pitting of the bucal surfaces. The teeth are also widely spaced.

Mental Capacity

Intelligence and mentality is typically not impaired in Morquio type A. However, progressive mental deficiency does occur in Morquio Type B.

 
What to Look For

Although the first 18 months are characterized by relatively normal development, beyond this age, Morquio patients tend to decline, especially in proportionate growth and mobility.

Any change in walking ability, endurance, or breathing merits further assessment by a physician to rule out spinal cord compression. Specific neurological symptoms such as tingling or numbness in the arms or legs, weakness, shooting leg or arm pain, or problems controlling bladder/ bowel function should be investigated further.

Considering that eye and teeth problems are especially associated with Morquio Syndrome, ophthalmologic consultation and dental examinations are recommended for early detection and treatment.

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. Cole, D.E.C. Fukuda, S. Gordon, B.A. Rip, J.W. LeCouteur, A.N. Rupar, C.A. Tomatsu, S. Ogawa, T. Sukegawa, K. Orii, T. Heteroallelic Missense Mutations of the Galactosamine-6-Sulfate Sulfatase (GALNS) Gene is a Mild Form of Morquio Disease (MPS IVA) American Journal of Medical Genetics. 63: 558-565. 1996.
  2. Giugliani, R. Jackson M. Skinner S.J. Vimal C. M. Fensom A. H. Fahmy A. Sjövall. Beson, P. F. Progressive mental regression in siblings with Morquio disease Type B (mucopolysaccharidosis IV B). Clinical Genetics. 32: 313-325. 1987.
  3. Greaves, M.W. Inman, P. M. Cutaneous Changes in the Morquio Syndrome. Br. J. Derm. 81: 29-36. 1969.
  4. Jones, Kenneth L. Recognizable Patterns of Human Malformation. Philadelphia, PA: Elsevier Saunders. 2006
  5. Kopits, Steven E. Orthropedic Complications of Dwarfism. Clinical Orthopedics and Related Research. 144: 153-179. 1976.
  6. Matalon, R.; Arbogast, B.; Dorfman, A. Morquios syndrome: a deficiency of chondroitin sulfate N-acetylhexosamine sulfate sulfatase. (Abstract) Pediat. Res. 8: 436, 1974.
  7. Nelson, J.; Crowhurst, J.; Carey, B.; Greed, L. Incidence of the mucopolysaccharidoses in western Australia. Am. J. Med. Genet. 123A: 310-313, 2003.
  8. Scott, Charles I. Dwarfism. Clinical Symposium, 1988; 40(1):9-10.
  9. Spranger, Jurgen W. Brill, Paula W. Poznanski, Andrew. Bone Dysplasias: An Atlas of Genetic Disorder of Skeletal Development. Oxford: Oxford University Press. 2002.
  10. Taybi, Hooshang. Lachman, Ralph S. Radiology of Syndromes, Metabolic Disorders, and Skeletal Dysplasias. St. Louis, MO: Mosby-Year Book, Inc. 1996.

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All About Genetics

What do you know about your family tree? Have any of your relatives had health problems that tend to run in families? Which of these problems affected your parents or grandparents? Which ones affect you or your brothers or sisters now? Which problems might you pass on to your children?

Thanks to advances in medical research, doctors now have the tools to understand much about how certain illnesses, or increased risks for certain illnesses, pass from generation to generation. Here are some basics about genetics.

Genes and Chromosomes

Each of us has a unique set of chemical blueprints affecting how our body looks and functions. These blueprints are contained in our DNA (deoxyribonucleic acid), long, spiral-shaped molecules found inside every cell. DNA carries the codes for genetic information and is made of linked subunits called nucleotides. Each nucleotide contains a phosphate molecule, a sugar molecule (deoxyribose), and one of four so-called "coding" molecules called bases (adenine, guanine, cytosine, or thymidine). The sequence of these four bases determines each genetic code.

The segments of DNA that contain the instructions for making specific body proteins are called genes. Scientists believe that human DNA carries about 25,000 protein-coding genes. Each gene may be thought of as a "recipe" you'd find in cookbook. Some are recipes for creating physical features, like brown eyes or curly hair. Others are recipes to tell the body how to produce important chemicals called enzymes (which help control the chemical reactions in the body).

Along the segments of our DNA, genes are neatly packaged within structures called chromosomes. Every human cell contains 46 chromosomes, arranged as 23 pairs (called autosomes), with one member of each pair inherited from each parent at the time of conception. After conception, the chromosomes duplicate again and again to pass on the same genetic information to each new cell in the developing child. Twenty-two autosomes are the same in males and females. In addition, females have two X chromosomes and males have one X and one Y chromosome. The X and the Y are known as sex chromosomes.

Human chromosomes are large enough to be seen with a high-powered microscope, and the 23 pairs can be identified according to differences in their size, shape, and the way they pick up special laboratory dyes.

Genetic Problems

Errors to the genetic code or "gene recipe" can happen in a variety of ways. Sometimes information is missing from the code, other times codes have too much information, or have information that's in the wrong order.

These errors can be big (for example, if a recipe is missing many ingredients — or all of them) or small (if just one ingredient is missing). But regardless of whether the error is big or small, the outcome can be significant and cause a person to have a disability or at risk of a shortened life span.

Abnormal Numbers of Chromosomes

When a mistake occurs during cell division, it can cause an error in the number of chromosomes a person has. The developing embryo then grows from cells that have either too many chromosomes or not enough.

In trisomy, for example, there are three copies of one particular chromosome instead of the normal two (one from each parent). Trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) are examples of this type of genetic problem.

Trisomy 18 affects 1 out of every 7,500 births. Children with this syndrome have a low birth weight and a small head, mouth, and jaw. Their hands typically form clenched fists with fingers that overlap. They also might have malformations involving the hips and feet, heart and kidney problems, and intellectual disability (also called mental retardation). Only about 5% of these children are expected to live longer than 1 year.

Trisomy 13 affects 1 out of every 15,000 to 25,000 births. Children with this condition often have cleft lip and palate, extra fingers or toes, foot abnormalities, and many different structural abnormalities of the skull and face. This condition also can cause malformations of the ribs, heart, abdominal organs, and sex organs. Long-term survival is unlikely but possible.

In monosomy, another form of numerical error, one member of a chromosome pair is missing. So there are too few chromosomes rather than too many. A baby with a missing autosome has little chance of survival. However, a baby with a missing sex chromosome can survive in certain cases. For example, girls with Turner syndrome — who are born with just one X chromosome — can live normal, productive lives as long as they receive medical care for any health problems associated with their condition.

Deletions, Translocations, and Inversions

Sometimes it's not the number of chromosomes that's the problem, but that the chromosomes have something wrong with them, like an extra or missing part. When a part is missing, it's called a deletion (if it's visible under a microscope) and a microdeletion (if it's not visible). Microdeletions are so small that they may involve only a few genes on a chromosome.

Some genetic disorders caused by deletions and microdeletions include Wolf-Hirschhorn syndrome (affects chromosome 4), Cri-du-chat syndrome (chromosome 5), DiGeorge syndrome (chromosome 22), and Williams syndrome (chromosome 7).

In translocations (which affect about 1 in every 400 newborns), bits of chromosomes shift from one chromosome to another. Most translocations are "balanced," which means there is no gain or loss of genetic material. But some are "unbalanced," which means there may be too much genetic material in some places and not enough in others. With inversions (which affect about 1 in every 100 newborns), small parts of the DNA code seem to be snipped out, flipped over, and reinserted. Translocations may be either inherited from a parent or happen spontaneously in a child's own chromosomes.

Both balanced translocations and inversions typically cause no malformations or developmental problems in the kids who have them. However, those with either translocations or inversions who wish to become parents may have an increased risk of miscarriage or chromosome abnormalities in their own children. Unbalanced translocations or inversions are associated with developmental and/or physical abnormalities.

Sex Chromosomes

Genetic problems also occur when abnormalities affect the sex chromosomes. Normally, a child will be a male if he inherits one X chromosome from his mother and one Y chromosome from his father. A child will be a female if she inherits a double dose of X (one from each parent) and no Y.

Sometimes, however, children are born with only one sex chromosome (usually a single X) or with an extra X or Y. Girls with Turner syndrome are born with only one X chromosome, whereas boys with Klinefelter syndrome are born with 1 or more extra X chromosomes ( XXY or XXXY).

Sometimes, too, a genetic problem is X-linked, meaning that it is associated with an abnormality carried on the X chromosome. Fragile X syndrome, which causes intellectual disability in boys, is one such disorder. Other diseases that are caused by abnormalities on the X chromosome include hemophilia and Duchenne muscular dystrophy.

Females may be carriers of these diseases, but because they also inherit a normal X chromosome, the effects of the gene change on the affected X is minimized. Males, on the other hand, only have one X chromosome and are almost always the ones who have the substantial effects of the X-linked disorder.

Gene Mutations

Some genetic problems are caused by a single gene that is present but altered in some way. Such changes in genes are called mutations. When there is a mutation in a gene, the number and appearance of the chromosomes is usually still normal.

To pinpoint the defective gene, scientists use sophisticated DNA screening techniques. Genetic illnesses caused by a single problem gene include phenylketonuria (PKU), cystic fibrosis, sickle cell disease, Tay-Sachs disease, and achondroplasia (a type of dwarfism).

Although experts used to think that no more than 3% of all human diseases were caused by errors in a single gene, new research shows that this is an underestimate. Within the last few years, scientists have discovered genetic links to many different diseases that weren't originally thought of as genetic, including Parkinson's disease, Alzheimer's disease, heart disease, diabetes, and several different types of cancer. Alterations in these genes are thought to increase one's risk of developing these conditions.

Oncogenes (Cancer-Causing Genes)

Researchers have identified about 50 cancer-causing genes that greatly increase a person's odds of developing cancer. By using sophisticated screening tools, doctors may be able to identify who has these genetic mutations, and determine who is at risk.

For example, scientists have determined that colorectal cancer is sometimes associated with mutations in a gene called APC. They've also discovered that abnormalities in the BRCA1 and BRCA2 gene give women a 50% chance of developing breast cancer and an increased risk for ovarian tumors.

People who are known to have these gene mutations now can be carefully monitored by their doctors. If problems develop, they're more likely to get treated for cancer earlier than if they hadn't known of their risk, and this can increase their odds of survival.

New Discoveries, Better Care

Scientists have made major strides in the field of genetics over the last two decades. The mapping of the human genome and the discovery of many disease-causing genes has led to a better understanding of the human body, enabling doctors to provide better care to their patients and increasing the quality of life for people (and their families) living with genetic conditions.

Reviewed by: Nina Powell-Hamilton, MD
Date reviewed: April 2013