There are hundreds of different genetic conditions associated with hearing loss. Inherited genetic conditions can often be described as autosomal dominant, autosomal recessive, X-linked, or mitochondrial. An autosomal dominant disorder requires that only one parent carry the gene for a child to be affected. However, an autosomal recessive disorder needs both parents to be carriers of the gene for a child to inherit the condition. X-linked disorders can be either dominant or recessive. A dominant X-linked disorder will affect more females, while a recessive X-linked condition will impact more males. Lastly, mitochondrial genetic disorders can impact both females and males, but are passed down only by females.4
This article will discuss Stickler syndrome, a disorder that includes six different variations. Stickler syndrome is unique in that it can be either autosomal dominant or autosomal recessive. Types I – III are autosomal dominant, while types IV – VI are autosomal recessive. Approximately 80% – 90% of cases are type I.6
What is Stickler syndrome? What Causes it?
Stickler syndrome was first identified in 1965 by Gunnar Stickler, who reported it as “hereditary progressive arthro-ophthalmopathy.”8 It is a rare and progressive disorder that primarily impacts three body functions and systems: eyesight, hearing, and bone/joint abnormalities.7 This disorder is also associated with distinctive facial differences.6 Due to the progressive nature of Stickler syndrome, symptoms become more severe as a person ages.3
Stickler syndrome is caused by changes in the genes associated with collagen in the body. Collagen is one of the many building blocks that make up bones, muscles, skin, and tendons.7 The type of collagen most commonly affected by Stickler syndrome are those that make up joint cartilage and the vitreous material within the eyes.5 Stickler syndrome type I is caused by differences in the COL2A1 gene, which is one of many genes responsible for creating collagen.6
What are the Signs and Symptoms of Stickler Syndrome? How Common Is It?
The features of Stickler syndrome differ from person to person, but the common features associated with the disorder are differences in bones and joints, hearing loss, vision loss, facial differences, and cleft palate.
This disorder affects approximately 1 out of every 7,500 births, but may be misdiagnosed or undiagnosed if symptoms are mild.3 The most outwardly noticeable signs of Stickler syndrome are the facial differences. According to the Mayo Clinic, a person with Stickler syndrome may have a small or receding chin, a small nose, scooped-out or flat facial features, and prominent eyes.5
What are the Risk Factors for Stickler Syndrome?
As previously discussed, Stickler syndrome is a unique genetic condition that can be either autosomal dominant or autosomal recessive. Up to 90% of cases of Stickler syndrome are type I, being autosomal dominant.6 This means that if a child has one parent with autosomal dominant Stickler syndrome, they have a 50% chance of inheriting the disorder. If both parents have autosomal recessive Stickler syndrome, the child is at risk.5 Both sexes are equally at risk for inheriting Stickler syndrome.1
How is Stickler Syndrome Diagnosed?
Some infants and children may present with mild symptoms, which may lead to a delayed diagnosis or even a misdiagnosis.3 Genetic testing is used in many cases to confirm the diagnosis of Stickler syndrome. Genetic testing can also be used during family planning to determine if a person is at risk of passing on the gene if there is not a clear hereditary pattern in a person’s family history.5 The traits associated with Stickler syndrome may be associated with different genetic diagnosis. In order to diagnose Stickler syndrome, the following disorders should be ruled out: Marfan syndrome, Loeys-Dietz syndrome, Wagner syndrome, Czech dysplasia, Knobloch syndrome, autosomal dominant rhegmatogenous retinal detachment, Donnai-Barrow syndrome, and Ehlers-Danlos syndrome.8
In addition to genetic testing, Stickler syndrome is diagnosed by multidisciplinary teams to evaluate the structures associated with the disorder. For example, bone and joint abnormalities can be assessed with x-rays and other imaging techniques. Vision loss is managed and assessed by opthamologists, and otolaryngologists and audiologists are responsible for evaluating hearing and ear abnormalities.
What Complications are Associated with Stickler Syndrome?
According to the Mayo Clinic, there are seven main potential complications associated with Stickler syndrome: difficulty breathing or feeding, blindness, ear infections, hearing loss, heart problems, bone/joint abnormalities, and dental problems.5
Stickler syndrome causes bone abnormalities, often resulting in small upper (maxilla) and lower (mandible) jaws.7 In addition to small jaws, an individual with Stickler syndrome’s tongue may be placed further back in the mouth than the average person. This can cause breathing difficulties due to blockage of the airway.7 A cleft palate, or a hole in the roof of the mouth, is also common in those with Stickler syndrome, which can also contribute to breathing and feeding problems.3 One meta analysis indicated that approximately 43% of individuals with Stickler syndrome have a cleft palate.1
Individuals with Stickler syndrome often suffer from progressive vision loss, including myopia, cataracts, retinal detachment, astigmatism, and glaucoma.3 The most common cause of retinal detachment in children is Stickler syndrome, and cataracts may be present at birth. Cataracts are clouding of the lens of the eye, which can result in blurred vision. A pressure buildup in the eye (glaucoma) can cause damage to the nerves that connect the eyes to the brain. Early treatment of glaucoma may prevent severe vision loss.7 Stickler syndrome type I has the highest risk of eye abnormalities, including retinal detachment. Type III does not include eye abnormalities.6
Hearing loss is common in children with Stickler syndrome. The hearing loss can be sensorineural, conductive, or mixed. Sensorineural hearing loss occurs due to damage to the cochlea (inner ear) or the nerve connecting the cochlea to the brain. Conductive hearing loss is caused by damage or abnormalities to the outer ear and middle ear. Mixed hearing loss is a combination of both sensorineural and conductive types. The cleft palate associated with Stickler syndrome can put a child at a high risk of developing middle ear infections due to fluid buildup behind the eardrum, resulting in conductive hearing loss.7 A meta analysis of 46 articles on Stickler syndrome revealed that approximately 46% of the patients under the age of 18 had conductive hearing loss, while approximately 23% of patients over the age of 18 had conductive hearing loss.1 Stickler syndrome type I is commonly associated with hearing loss, while types II and III are at a higher risk of severe hearing loss.6
In a systematic review that assessed 313 patients with Stickler syndrome, 63% of the individuals had hearing loss. 67.8% had sensorineural hearing loss, 14.1% had conductive hearing loss, and 18.1% had mixed hearing loss.1 74% of patients with a cleft palate associated with Stickler syndrome had hearing loss, while 54% of those without a cleft palate had hearing loss.
One of the genes impacted by Stickler syndrome, COL2A1, is present in many of the structures that make up the inner ear. A defect in this gene can cause a breakdown in bodily functions. The inner ear contains a structure called the tectorial membrane, made up of collagen fibers. A person with Stickler syndrome is at risk for damage to this membrane, leading to sensorineural hearing loss.1 The audiometric presentation of a person with Stickler syndrome is often in the higher frequencies, and it progresses over time. However, individuals with the disorder may develop other audiometric configurations, such as trough shaped audiograms with more hearing loss in the mid frequencies. While the sensorineural hearing loss in those with Stickler syndrome is progressive, it is typically mild to moderate, and it rarely evolves to a severe or profound degree.1
Approximately 50% of individuals with Stickler syndrome have a heart defect called mitral valve prolapse. This defect results in the valve between the heart’s left upper and lower chambers to close improperly. Symptoms of mitral valve prolapse include elevated or irregular heartbeat, fatigue, and shortness of breath. The majority of those with mitral valve prolapse do not require treatment, but some may need to take medications or undergo surgical corrections.3
The joint and bone abnormalities caused by Stickler syndrome can cause loose joints (hypermobility), arthritis, enlarged joints, and a short stature.7 Hypermobility is more common in children with Stickler syndrome, but it is often resolved in adulthood.2 Approximately 30% of individuals with the disorder develop arthritis between 30 – 40 years of age.7
The dental problems associated with Stickler syndrome may cause a misalignment of the jaw, or crowding of the teeth due to small mouths associated with the disorder.7 Those with severe dental abnormalities may need corrective surgery and/or significant orthodontic treatment.
How is Stickler Syndrome Managed or Treated?
While there is no cure for Stickler syndrome, there are treatments available to manage some of the symptoms. One treatment includes surgical corrections of physical abnormalities. For example, if a child with Stickler syndrome was born with a cleft palate, it is often corrected with surgery.
As previously stated, a person with Stickler syndrome may have a small or receding jaw that can lead to feeding and speaking problems. Jaw lengthening surgery may be recommended. This is completed by breaking the lower jawbone and surgically placing a device used to stretch the structure as the person ages and as they heal.5 Surgery to correct a cleft palate can be performed at approximately nine months of age.3 Individuals with severe breathing difficulty caused by Stickler syndrome may require a tracheostomy, or a breathing tube placed in the windpipe.7 Speech difficulties may be present in children with Stickler syndrome due to the facial abnormalities and cleft palates, which may require assessment and treatment by a speech language pathologist. Dental problems associated with Stickler syndrome may be corrected with surgery and/or braces.7
Eye surgeries may be recommended in cases of retinal detachment. Retinal detachment is considered a medical emergency, and a delay of surgical correction can lead to permanent blindness.5 Individuals with myopia (nearsightedness) caused by Stickler syndrome may need corrective lenses in the form of glasses or contacts. Severe cataracts can be corrected by the surgical removal of the lens of the eye and to be replaced by an artificial lens. Individuals with Stickler syndrome should have an opthamologist check their eyes annually, or more often if complications are detected.7
Children with Stickler syndrome are at high risk for developing middle ear infections, which can be treated with pressure equalization tubes. These tubes are hollow in nature and made up of soft material. The purpose of pressure equalization tubes is to allow for assistance in the drainage of the fluid that builds up behind the eardrum that leads to middle ear infections. A person may need short term or long term pressure equalization tubes, depending on the severity and length of the middle ear infections. This is determined by a physician, more specifically an otolaryngologist or an “ear, nose, and throat” (ENT) physician.5
In addition to treating middle ear infections associated with Stickler syndrome, some individuals may require hearing aids. Patients with Stickler syndrome should have their hearing checked by an audiologist every six months up until six years of age, then annually. If there are increased concerns of hearing loss, an individual may require more than one hearing test per year.7
Due to the abnormalities in collagen caused by Stickler syndrome, a person may develop a spinal curve, such as scoliosis or kyphosis. The severity of the curve will determine if a person should have surgical corrections, or if it can be treated with a brace.5 10% of individuals with Stickler syndrome are impacted by scoliosis and/or kyphosis.7
In addition to abnormalities in the curvature of the spine, joint abnormalities are common in individuals with Stickler syndrome. These joint issues may cause early-onset arthritis, which might require joint replacements. Physical therapy may be recommended to help strengthen joints.
Can Stickler Syndrome be Prevented?
As previously discussed, Stickler syndrome can be autosomal dominant or recessive, and may be prevented with family planning after genetic testing.
While there is no cure for Stickler syndrome, steps can be taken to prevent complications. Due to the joint and abnormalities, both children and adults should avoid contact sports that cause excess pressure and stress to the joints.5 Avoiding contact sports can also prevent the likelihood of retinal detachment.7
What is the Prognosis (Outlook) for People with Stickler Syndrome?
While Stickler syndrome does not impact an individual’s life expectancy, it is considered a progressive disorder. However, with the treatments discussed previously, a person with Stickler syndrome can live a happy and healthy life.
To conclude, Stickler syndrome is a complex and progressive genetic disorder associated with blindness, hearing loss, and joint abnormalities. Those diagnosed with the disorder should work with a multidisciplinary team for assessments and treatments. This team may include the following: ophthalmology, rheumatology, audiology, otolaryngology, speech language pathology, genetic counseling, cardiology, physical therapy, and more. With treatment and close monitoring, a person with Stickler syndrome can lead a happy and healthy life.
References:
1Acke, F., Dhooge, I., Malfait, F., & De Leenheer, E. (2012). Hearing impairment in Stickler syndrome: A systematic review. Orphanet Journal of Rare Diseases, 7.
2Boothe, M., Morris, B., & Robin, N. (2020). Stickler syndrome: A review of clinical manifestations and the genetics evaluation. Journal of Personalized Medicine, 10.
3Boston Children’s Hospital. (2022). Conditions: Stickler syndrome. Boston Children’s Hospital.
4Genetic Alliance. (2009). Appendix E. Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals. The New York-Mid-Atlantic Consortium for Genetic and Newborn Screening Services.
5Mayo Clinic. (2021). Diseases and conditions: Stickler syndrome. Mayo Clinic.
6MedlinePlus. (2022). Genetic conditions: Stickler syndrome. MedlinePlus.
7Seattle Children’s Hospital. (2022). Conditions: Stickler syndrome. Seattle Children’s Hospital.
8Soh, Z., Richards, A. J., McNinch, A., Alexander, P., & Martin, H. (2022). Dominant Stickler syndrome. Genes, 13.