Schwartz-Jampel syndrome (SJS) is a rare genetic disorder characterized by abnormalities of the skeletal muscles, including muscle weakness and stiffness (myotonic myopathy); abnormal bone development (bone dysplasia); permanent bending or extension of certain joints in a fixed position (joint contractures); and/or growth delays resulting in abnormally short stature (dwarfism). Affected individuals may also have small, fixed facial features and various abnormalities of the eyes, some of which may cause impaired vision. The range and severity of symptoms may vary from case to case. Two types of the disorder have been identified that may be differentiated by age of onset and other factors. SJS type 1, which is considered the classical form of the disorder, may become apparent during early to late infancy or childhood. SJS type 2, a more rare form of the disorder, is typically recognized at birth (congenital). Most researchers now believe that SJS type 2 is actually the same disorder as Stuve-Wiedemann syndrome and not a form of SJS. (For more information on Stuve-Wiedemann syndrome see the Related Disorders section of this report.)
SJS is thought to be inherited as an autosomal recessive trait. However, some cases reported in the medical literature suggest an autosomal dominant inheritance pattern.
SJS is primarily characterized by abnormalities of skeletal muscle, bone, and cartilage; malformations of the eyes and the face; and growth delays. In some cases, additional abnormalities may also be present. The range and severity of associated symptoms and physical findings varies from case to case, depending upon the form of the disorder present and other factors. Two forms of the disorder have been recognized, which are known as SJS types 1 and 2. SJS type 1, which is considered the classical form of the disorder, may be recognized during early to late infancy or childhood, whereas SJS type 2 is apparent at birth (congenital).
Infants with classical or type 1 SJS may have a normal or low birth weight. From the first or second year of life through childhood, an affected child’s growth rate may be below the normal range. Although the growth rate may increase during puberty, adult height may still be below the normal range; as a result, such affected individuals may have abnormally short stature (dwarfism). In addition to possible growth delays, most infants with SJS are delayed in reaching developmental milestones, such as crawling, sitting, walking, etc. (delayed motor development). However, after the age of about two years, their motor abilities may improve. Mental development is generally normal.
The skeletal muscle abnormalities associated with SJS may be recognized at birth or infancy or may become apparent within the second year of life. Affected children may have muscle stiffness and weakness, an inability to relax certain muscles after they have contracted (myotonic myopathy), and abnormally small skeletal muscles. In addition, several joints may become fixed in a permanently bent or extended position (joint contractures) due to shortening of muscle fibers. In some cases, the symptoms of myotonic myopathy associated with SJS may gradually diminish.
In most cases, individuals with classical SJS also have abnormalities of bone and cartilage growth (chondrodystrophy). The layers of cartilage that separate the shaft of a long bone (diaphysis) from its growing end (epiphyseal plate or growth plate) may develop abnormally (epiphyseal dysplasia). (Long bone refers to bones in the arms and legs.) As a result, the growing end (epiphysis) of the long bone may flatten and fragment. Such flattening of the epiphysis of the thighbone (femur) may contribute to or occur in association with abnormal development of the hipbone (hip dysplasia).
Additional skeletal abnormalities may also occur in children with classical Schwartz-Jampel syndrome. Affected individuals may have an abnormally short neck, malformation of the hip (hip dysplasia), and/or a sideways and front-to-back curvature of the spine (kyphoscoliosis). In addition, the breastbone (sternum) may be abnormally prominent (“pigeon breast” or pectus carinatum).
Some researchers suggest that the classical form of SJS may be divided into two distinct subgroups, depending upon the severity of associated skeletal abnormalities. SJS type 1A, which may be recognized during early childhood, is characterized by mild skeletal changes (skeletal dysplasia) that occur secondary to skeletal muscle abnormalities. Type 1B may be recognized at birth or early infancy based upon primary, more pronounced abnormalities of bone development (primary skeletal dysplasia) in association with muscle defects.
Many of the musculoskeletal abnormalities occurring in association with classical SJS (e.g., myotonia, joint contractures, hip dysplasia, etc.) may make it difficult for affected individuals to perform certain voluntary movements. For example, many may have difficulty walking independently.
Within the first or second year of life, facial abnormalities associated with classical SJS also become apparent. The mouth and chin may appear abnormally small; the face may appear flat; facial expressions may seem fixed or mask-like; and the face may have a characteristic “pinched” appearance. In addition, the entire face may seem small in relation to the size of the head. Affected individuals may also have abnormally low-set ears.
Many individuals with classical SJS also have several eye (ocular) abnormalities. The front transparent region of the eye through which light passes may be small (microcornea) or the entire eye may appear unusually small (microphthalmia). The opening between the upper and lower eyelids (palpebral fissures) may be narrow and short (blepharophimosis), and the lids may have two or more rows of eyelashes. Affected individuals may also have nearsightedness (myopia), clouding of the lenses of the eyes (juvenile cataracts), and/or intermittent, involuntary contractions or spasms of the muscles around the eyes (blepharospasm). Such eye abnormalities may result in varying degrees of visual impairment. In cases of blepharospasm, an inability to open the eyelids due to involuntary muscle spasms may result in functional blindness. The degree of visual impairment in affected individuals depends upon the severity and/or combination of eye abnormalities present. (For more information on blepharospasm, please see the Related Disorders section below.)
In some cases, individuals with classical SJS may have additional abnormalities. Affected individuals may have high-pitched voices and their speech may be difficult to understand. In some cases, there may be protrusion of portions of the large intestine through an abnormal opening in muscles of the groin (inguinal hernia) or the abdominal wall where the umbilical cord joins the fetal abdomen (umbilical hernia). In addition, some affected males may have unusually small testes. Individuals with the disorder may also be prone to repeated respiratory infections.
Some individuals with SJS may be at risk for malignant hyperthermia, a condition in which exposure to certain anesthetics or muscle relaxants may cause a sudden rise in body temperature (hyperthermia), muscle twitching and stiffness, and other symptoms. Without appropriate treatment, life-threatening symptoms may result. (For more information on this condition, please see the Related Disorders section of this report.)
As mentioned above, researchers have recognized a second, more severe form of Schwartz-Jampel syndrome, known as SJS type 2. Because this form of the disorder is apparent at birth, it is also often referred to as “neonatal” SJS. SJS type 2 is characterized by distinctive facial abnormalities, including a “pursed” appearance of the mouth; muscle weakness; and abnormalities of the growing ends of the long bones (metaphyses) of the arms and legs (limbs), associated bowing of the limbs (campomelic-metaphyseal skeletal dysplasia), and short stature. Additional findings typically include permanent bending or extension of several joints in various fixed postures (joint contractures) at birth. Affected infants may also have feeding, swallowing, and breathing difficulties and be prone to sudden and severe rises in body temperature (hyperthermia), potentially leading to life-threatening complications. Many researchers suggest that SJS type 2 and a disorder known as Stuve-Wiedemann syndrome are the same disease entity.
SJS types 1 and 2 are both thought to have autosomal recessive inheritance. Genetic diseases are determined by two genes, one received from the father and one from the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%.
Some individuals with SJS types 1 and 2 have had parents who were related by blood (consanguineous). All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Researchers have determined that the classical form of SJS may be caused by changes (mutations) of a gene encoding perlecan located on the short arm (p) of chromosome 1 (1p36.1-p34). Perlecan is a large heparan sulfate proteoglycan and plays a role in neuromuscular function and cartilage formation. Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males, and two X chromosomes for females. Each chromosome has a short arm designated as “p” and a long arm identified by the letter “q.” Chromosomes are further subdivided into many bands that are numbered.
Genetic evaluation of at least three families (kindreds) with individuals affected by the severe neonatal form of SJS (type 2) has determined that those with the disorder did not have mutations of the disease gene located at 1p36.1-p34 (discussed above). Accordingly, researchers indicate that SJS may result from mutations of different genes (genetic heterogeneity).
SJS (SJS) types 1 and 2 are rare disorders that appear to affect males and females in equal numbers. More than 85 cases have been reported in the medical literature, including individuals affected by the classical (type 1) and the more severe neonatal form (type 2) of the disorder. SJS type 2 appears to be most common in individuals of United Arab Emirates descent. Depending upon the form of the disorder present, associated symptoms and findings may be recognized at birth or may become apparent during infancy or within the second year of life.
In rare cases, SJS may be diagnosed before birth (prenatally) through the use of specialized tests such as ultrasound. During ultrasonography, reflected sound waves are used to create an image of the developing fetus. Such imaging studies may reveal characteristic findings that suggest SJS or other developmental abnormalities in the fetus.
SJS is usually diagnosed at birth or within the first or second year of life. Such a diagnosis may be confirmed based upon a thorough clinical evaluation, a detailed patient history, and a variety of specialized tests. The presence of myotonic myopathy, a primary finding associated with the disorder, may be confirmed through several tests, including electromyograms (EMG). An EMG is a test that records electrical activity in skeletal muscles at rest and during muscle contraction. In cases of myotonic myopathy, an EMG may demonstrate continuous electrical activity within muscle fibers, even while at rest. Other specialized tests used to confirm myotonic myopathy may include studies that measure the levels of certain enzymes in the fluid portion of the blood (serum enzymes) and/or the surgical removal (biopsy) and microscopic examination (light and/or electron microscopy) of small samples of muscle tissue. The presence of skeletal abnormalities often associated with SJS may be confirmed by specialized imaging studies and other testing.
The treatment of SJS is directed toward the specific symptoms that are apparent in each individual. Pediatricians; physicians who diagnose and treat diseases of the eye (ophthalmologists); specialists who diagnose and treat skeletal abnormalities (orthopedists); surgeons; physical therapists; and/or other health care professionals may need to work together to ensure a comprehensive approach to treatment.
Specific therapies for the treatment of SJS are symptomatic and supportive. In some infants with the severe neonatal form of the disorder (SJS Type 2), treatment may require special supportive therapies to ensure the appropriate intake of nutrients, oxygen therapy, measures to help prevent or appropriately treat episodes of hyperthermia, and other therapies as required.
In individuals with SJS, various orthopedic techniques, including surgery, may be used to help treat and/or correct musculoskeletal abnormalities, such as joint contractures, kyphoscoliosis, and/or hip dysplasia. Because the skeletal changes associated with hip dysplasia may worsen during childhood, early orthopedic treatment may be essential in preventing such a progression of symptoms. In some cases of hip dysplasia, an artificial device (prosthetic) may be used to replace the hip joint. Physical therapy in combination with such surgical and supportive measures may improve an affected individual's ability to walk and perform other movements independently (mobility). In addition, in some individuals with SJS, depending upon the visual abnormalities that are present, corrective glasses, contact lenses, other supportive methods, and/or surgery may be used to help improve vision.
Additional therapeutic and/or supportive measures may be necessary in some cases. Physicians may regularly monitor affected individuals and recommend preventive measures for those who may be prone to respiratory infections. In individuals with protrusion of portions of the large intestine through an abnormal opening in muscles of the groin (inguinal hernia), surgical correction of the hernia may be necessary. If there is a small, abnormal opening in muscles of the abdominal wall where the umbilical cord joined the fetal abdomen (umbilical hernia), the abnormal opening may close on its own (spontaneously) within one or two years; however, if the umbilical hernia is large, surgery may be required.
Some individuals with SJS may be at risk for Malignant Hyperthermia when exposed to certain anesthetics or muscle relaxants. This risk must be taken into consideration by surgeons, anesthesiologists, dentists, and other health care workers when making decisions concerning potential surgery and use of particular anesthetics. It must also be considered by primary care physicians and other health professionals when prescribing certain medications.
Early intervention is important in ensuring that children with SJS reach their potential. Special services that may be beneficial to affected children may include special remedial education, speech therapy, and other medical, social, and/or vocational services.
Genetic counseling will be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.
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