Stickler syndrome

Definition

Stickler syndrome is a disorder caused by a genetic malfunction in the tissue that connects bones, heart, eyes, and ears.

Description

Stickler syndrome, also known as hereditary arthroophthalmopathy, is a multisystem disorder that can affect the eyes and ears, skeleton and joints, and craniofacies. Symptoms may include myopia , cataract, and retinal detachment; hearing loss that is both conductive and sensorineural; midfacial underdevelopment and cleft palate; and mild spondyloepiphyseal dysplasia and/or arthritis. The collection of specific symptoms that make up the syndrome were first documented by Stickler et al., in a 1965 paper published in Mayo Clinic Proceedings titled "Hereditary Progressive Arthro-Opthalmopathy." The paper associated the syndrome's sight deterioration and joint changes. Subsequent research has redefined Stickler syndrome to include other symptoms.

Genetic profile

Stickler syndrome is associated with mutations in three genes: COL2A1 (chromosomal locus 12q13), COL11A1 (chromosomal locus 1p21), and COL11A2 (chromosomal locus 6p21). It is inherited in an autosomal dominant manner. The majority of individuals with Stickler syndrome inherited the abnormal allele from a parent, and the prevalence of new gene mutations is unknown. Individuals with Stickler syndrome have a 50% chance of passing on the abnormal gene to each offspring.

The syndrome can manifest itself differently within families. If the molecular genetic basis of Stickler syndrome has been established, molecular genetic testing can be used for clarification of each family member's genetic status and for prenatal testing.

A majority of cases are attributed to COL2A1 mutations. All COL2A1 mutations known to cause Stickler syndrome result in the formation of a premature termination codon within the type-II collagen gene. Mutations in COL11A1 have only recently been described, and COL11A2 mutations have been identified only in patients lacking ocular findings.

Although the syndrome is associated with mutations in the COL2A1, COL11A1, and COL11A2 genes, no linkage to any of these three known loci can be established in some rare cases with clinical findings consistent with Stickler syndrome. It is presumed that other, as yet unidentified, genes mutations also account for Stickler syndrome.

Genetically related disorders

There are a number of other phenotypes associated with mutations in COL2A1. Achondrogenesis type I is a fatal disorder characterized by absence of bone formation in the vertebral column, sacrum, and pubic bones, by the shortening of the limbs and trunk, and by prominent abdomen. Hypochondrogenesis is a milder variant of achondrogenesis. Spondyloepiphyseal dysplasia congenita, a disorder with skeletal changes more severe than in Stickler syndrome, manifests in significant short stature, flat facial profile, myopia, and vitreoretinal degeneration. Spondyloepimetaphyseal dysplasia Strudwick type is another skeletal disorder that manifests in severe short stature with severe protrusion of the sternum and scoliosis , cleft palate, and retinal detachment. A distinctive radiographic finding is irregular sclerotic changes, described as dappled, which are created by alternating zones of osteosclerosis and ostopenia in the metaphyses (ends) of the long bones. Spondyloperipheral dysplasia is a rare condition characterized by short stature and radiographic changes consistent with a spondyloepiphyseal dysplasia and brachydactyly . Kneist dysplasia is a disorder that manifests in disproportionate short stature, flat facial profile, myopia and vitreoretinal degeneration, cleft palate, backward and lateral curvature of the spine, and a variety of radiographic changes.

Other phenotypes associated with mutations in COL11A1 include Marshall syndrome , which manifests in ocular hypertelorism, hypoplasia of the maxilla and nasal bones, flat nasal bridge, and small upturned nasal tip. The flat facial profile of Marshall syndrome is usually evident into adulthood, unlike Stickler syndrome. Manifestations include radiographs demonstrating hypoplasia of the nasal sinuses and a thickened calvarium. Ocular manifestations include high myopia, fluid vitreous humor, and early onset cataracts. Sensorineural hearing loss is common and sometimes progressive. Cleft palate is seen both as isolated occurrence and as part of the Pierre-Robin sequence (micrognathia, cleft palate, and glossoptosis). Other manifestations include short stature and early onset arthritis, and skin manifestations that may include mild hypotrichosis and hypohidrosis.

Other phenotypes associated with mutations in COL11A2 include autosomal recessive oto-spondylometa-epiphyseal dysplasia, a disorder characterized by flat facial profile, cleft palate, and severe hearing loss. Anocular Stickler syndrome caused by COL11A2 mutations is close in similarity to this disorder. Weissenbach-Zweymuller syndrome has been characterized as neonatal Stickler syndrome but it is a separate entity from Stickler syndrome. Symptoms include midface hypoplasia with a flat nasal bridge, small upturned nasal tip, micrognathia, sensorineural hearing loss, and rhizomelic limb shortening. Radiographic findings include vertebral coronal clefts and dumbbell-shaped femora and humeri. Catch-up growth after age two or three is common and the skeletal findings become less apparent in later years.

Demographics

No studies have been done to determine Stickler syndrome prevalence. An approximate incidence of Stickler syndrome among newborns is estimated based on data on the incidence of Pierre-Robin sequence in newborns. One in 10,000 newborns have Pierre-Robin sequence, and 35% of these newborns subsequently develop signs or symptoms of Stickler syndrome. These data suggest that the incidence of Stickler syndrome among neonates is approximately one in 7,500.

Signs and symptoms

Stickler syndrome may affect the eyes and ears, skeleton and joints, and craniofacies. It may also be associated with coronary complications.

Ocular symptoms

Near-sightedness is a common symptom of Stickler syndrome. High myopia is detectable in newborns. Common problems also include astigmatism and cataracts. Risk of retinal detachment is higher than normal. Abnormalities of the vitreous humor, the colorless, transparent jelly that fills the eyeball, are also observed. Type 1, the more common vitreous abnormality, is characterized by a persistence of a vestigial vitreous gel in the space behind the lens, and is bordered by a folded membrane. Type 2, which is much less common, is characterized by sparse and irregularly thickened bundles throughout the vitreous cavity. These vitreous abnormalities can cause sight deterioration.

Auditory symptoms

Hearing impairment is common, and some degree of sensorineural hearing loss is found in 40% of patients. The degree of hearing impairment is variable, however, and may be progressive. Typically, the impairment is high tone and often subtle. Conductive hearing loss is also possible. It is known that the impairment is related to the expression of type II and IX collagen in the inner ear, but the exact mechanism for it is unclear. Hearing impairment may be secondary to the recurrent ear infections often associated with cleft palate, or it may be secondary to a disorder of the ossicles of the middle ear.

Skeletal symptoms

Skeletal manifestations are short stature relative to unaffected siblings, early-onset arthritis, and abnormalities at ends of long bones and vertebrae. Radiographic findings consistent with mild spondyloepiphyseal dysplasia. Some individuals have a physique similar to Marfan syndrome , but without tall stature. Young patients may exhibit joint laxity but it diminishes or even resolves completely with age. Early-onset arthritis is common and generally mild, mostly resulting in joint stiffness. Arthritis is sometimes severe, leading to joint replacement as early as the third or fourth decade.

Craniofacial findings

Several facial features are common with Stickler syndrome. A flat facial profile referred to as a "scooped out" face results from underdevelopment of the maxilla and nasal bridge, which can cause telecanthus and epicanthal folds. Flat cheeks, flat nasal bridge, small upper jaw, pronounced upper lip groove, small lower jaw, and palate abnormalities are possible, all in varying degrees. The nasal tip may be small and upturned, making the groove in the middle of the upper lip appear long. Micrognathia is common and may compromise the upper airway, necessitating tracheostomy. Midfacial hypoplasia is most pronounced in infants and young children, and older individuals may have a normal facial profile.

Coronary findings

Mitral valve prolapse may be associated with Stickler syndrome, but studies are, as yet, inconclusive about the connection.

Diagnosis

Stickler is believed to be a common syndrome in the United States and Europe, but only a fraction of cases are diagnosed since most patients have minor symptoms. Misdiagnosis may also occur because symptoms are not correlated as having a single cause. More than half of patients with Stickler syndrome are originally misdiagnosed according to one study.

While the diagnosis of Stickler syndrome is clinically based, clinical diagnostic criteria have not been established. Patients usually do not have all symptoms attributed to Stickler syndrome. The disorder should be considered in individuals with clinical findings in two or more of the following categories:

• Ophthalmologic. Congenital or early-onset cataract, myopia greater than -3 diopters, congenital vitreous anomaly, rhegmatogenous retinal detachment. Normal newborns are typically hyperopic (+1 diopter or greater), and so any degree of myopia in an at-risk newborn, such as one with Pierre-Robin sequence or an affected parent, is suggestive of the diagnosis of Stickler syndrome. Less common ophthalmological symptoms include paravascular pigmented lattice degeneration and cataracts.
• Craniofacial. Midface hypoplasia, depressed nasal bridge in childhood, anteverted nares (tipped or bent nasal cavity openings), split uvula, cleft hard palate, micrognathia, Pierre-Robin sequence).
• Audiologic. Sensorineural hearing loss.
• Joint. Hypermobility, mild spondyloepiphyseal dysplasia, precocious osteoarthritis.

It is appropriate to evaluate at-risk family members with a medical history and physical examination and ophthalmologic, audiologic, and radiographic assessments. Childhood photographs may be helpful in the evaluation of adults since craniofacial findings may become less distinctive with age.

Molecular genetic testing

Mutation analysis for COL2A1, COL11A1, and COL11A2 is available. Detection is performed by mutation scanning of the coding sequences. Stickler syndrome has been associated with stop mutations in COL2A1 and with missense and splicing mutations in all of the three genes. Because the meaning of a specific missense mutation within the gene coding sequence may not be clear, mutation detection in a parent is not advised without strong clinical support for the diagnosis.

Clinical findings can influence the order for testing the three genes. In patients with ocular findings, including type 1 congenital vitreous abnormality and mild hearing loss, COL2A1 may be tested first. In patients with typical ocular findings including type 2 congenital vitreous anomaly and significant hearing loss, COL11A1 may be tested first. In patients with hearing loss and craniofacial and joint manifestations but without ocular findings, COL11A2 may be tested first.

Prenatal testing

Before considering prenatal testing, its availability must be confirmed and prior testing of family members is usually necessary. Prenatal molecular genetic testing is not usually offered in the absence of a known disease-causing mutation in a parent. For fetuses at 50% risk for Stickler syndrome, a number of options for prenatal testing may exist. If an affected parent has a mutation in the gene COL2A1 or COL11A1, molecular genetic testing may be performed on cells obtained by chorionic villus sampling at 10–12 weeks gestation or amniocentesis at 16–18 weeks gestation. Alternatively, or in conjunction with molecular genetic testing, ultrasound examination can be performed at 19–20 weeks gestation to detect cleft palate. For fetuses with no known family history of Stickler syndrome in which cleft palate is detected, a three-generation pedigree may be obtained, and relatives who have findings suggestive of Stickler syndrome should be evaluated.

Treatment and management

Individuals diagnosed with Stickler syndrome, and individuals in whom the diagnosis cannot be excluded, should be followed for potential complications.

Evaluation by an ophthalmologist familiar with the ocular manifestations of Stickler syndrome is recommended. Individuals with known ocular complications may prefer to be followed by a vitreoretinal specialist. Patients should avoid activities that may lead to traumatic retinal detachment, such as contact sports. Patients should be advised of the symptoms associated with a retinal detachment and the need for immediate evaluation and treatment when such symptoms occur. Individuals from families with Stickler syndrome and a known COL2A1 or COL11A1 mutation who have not inherited the mutant allele do not need close ophthalmologic evaluation.

A baseline audiogram to test hearing should be performed when the diagnosis of Stickler syndrome is suspected. Follow-up audiologic evaluations are recommended in affected persons since hearing loss can be progressive.

Radiological examination may detect signs of mild spondyloepiphyseal dysplasia. Treatment is symptomatic, and includes over-the-counter anti-inflammatory medications before and after physical activity. No preventative therapies currently exist to minimize joint damage in affected individuals. In an effort to delay the onset of arthropathy, physicians may recommend avoiding physical activities that involve high impact to the joints, but no data support this recommendation.

Infants with Pierre-Robin sequence need immediate attention from otolaryngology and pediatric critical care specialists. Evaluation and management in a comprehensive craniofacial clinic that provides all the necessary services, including otolaryngology, plastic surgery, oral and maxillofacial surgery, pediatric dentistry, and orthodontics is recommended. Tracheostomy may be required, which involves placing a tube in the neck to facilitate breathing.

Middle ear infections (otitis media) may be a recurrent problem secondary to the palatal abnormalities, and ear tubes may be required. Micrognathia (small jaw) tends to become less prominent over time in most patients, allowing for removal of the tracheostomy. In some patients, however, significant micrognathia persists and causes orthodontic problems. In these patients, a mandibular advancement procedure may be required to correct jaw misalignment.

Cardiac care is recommended if complaints suggestive of mitral valve prolapse, such as episodic tachycardia and chest pain, are present. While the prevalence of mitral valve prolapse in Stickler syndrome is unclear, all affected individuals should be screened since individuals with this disorder need antibiotic prophylaxis for certain surgical procedures.

KEY TERMS

Glossoptosis

—Downward displacement or retraction of the tongue.

Spondyloepiphyseal dysplasia

—Abnormality of the vertebra and epiphyseal centers that causes a short trunk.

Prognosis

Prognosis is good under physician care. It is particularly important to receive regular vision and hearing exams. If retinal detachment is a risk, it may be advisable to avoid contact sports. Some craniofacial symptoms may improve with age.

Resources

PERIODICALS

Bowling, E. L., M. D, Brown, and T. V. Trundle. "The Stickler Syndrome: Case Reports and Literature Review." Optometry 71 (March 2000): 177+.

MacDonald, M. R., et al. "Reports on the Stickler Syndrome, An Autosomal Connective Tissue Disorder." Ear, Nose & Throat Journal 76 (October 1997): 706.

Snead, M. P., and J. R. Yates. "Clinical and Molecular Genetics of Stickler Syndrome." Journal of Medical Genetics 36 (May 1999): 353+.

Wilkin, D. J., et al. "Rapid Determination of COL2A1 Mutations in Individuals with Stickler Syndrome: Analysis of Potential Premature Termination Codons." American Journal of Medical Genetics 11 (September 2000): 141+.

ORGANIZATIONS

Stickler Involved People. 15 Angelina, Augusta, KS 67010. (316) 775-2993. <http://www.sticklers.org>.

Stickler Syndrome Support Group. PO Box 371, Walton-on-Thames, Surrey KT12 2YS, England. 44-01932 267635. <http://www.stickler.org.uk>.

WEBSITES

Robin, Nathaniel H., and Matthew L. Warman. "Stickler Syndrome." GeneClinics. University of Washington, Seattle. <http://www.geneclinics.org/profiles/stickler>.

"Stickler Syndrome." NORD—National Organization for Rare Disorders. <http://www.rarediseases.org>.

Jennifer F. Wilson, MS