1. NGS panel - Genetic testing for Stickler syndrome

Stickler syndrome

May 29, 2017

Clinical features

Stickler syndrome is a rare inherited connective tissue disorder characterized by distinctive facial appearance, ocular findings, hearing loss, and mild joint problems.

The characteristic flattened facial appearance in Stickler syndrome is a result of underdeveloped bones in the mid-face. Another characteristic feature of STK is “Pierre Robin sequence”1, a combination of cleft palate (opening in the roof of the mouth), glossoptosis (abnormal position of the tongue), and micrognathia (small lower jaw). This combination of features usually leads to feeding problems and difficulty breathing.

Thus, Stickler syndrome is a multisystem connective tissue disorder that can affect different tissues, including the eye, craniofacies, inner ear, skeleton, and joints.

Ocular findings in Stickler syndrome include the following:

  • High myopia (>−3 diopters) that is non-progressive and detectable in the newborn period2;
  • Vitreous abnormalities that can have the more common membranous form (type 1), characterized by a persistence of vestigial vitreous gel in the space behind the lens that is bordered by a folded membrane; and thze less common type 2 form, “beaded”, characterized by thickened bundles throughout the vitreous cavity1, 2.
  • Posterior chorioretinal atrophy, that was previously associated only with Wagner disease3.

Facial/craniofacial findings include the following characteristics1:

  • Flat facial profile caused by underdevelopment of the nasal bridge and maxilla (upper jawbone), which can cause telecanthus (increased distance between medial canthi of the eyes) and epicanthal folds (skin fold of the upper eyelid)
  • Midface retrusion (vertical shortening of the infraorbital regions and increased concavity of the face) is most pronounced in infants and young children, whereas older STK-affected individuals may have a normal facial profile
  • The nasal tip is small and upturned, making the philtrum appear long
  • Micrognathia is common and may be associated with cleft palate as part of the Pierre Robin sequence. The degree of micrognathia may compromise the upper airway, necessitating tracheostomy.
  • Cleft palate may be seen as an isolated phenomenon, e.g. in the absence of micrognathia.

Hearing impairment is common in STK-affected individuals and it can be of variable degree and is commonly progressive:

  • Sensorineural hearing impairment with typically high-tone is diagnosed in 40% of individuals1, 2
  • Overall sensorineural hearing loss in Stickler syndrome is mild in most cases and it is not significantly progressive. The exact pathophysiological mechanism is unclear; however it is most probably associated with the expression of type II and IX collagen in the inner ear2, 4.
  • Conductive hearing loss is observed in STK-affected individuals secondary to the recurrent ear infections that are often associated with cleft palate and/or may be secondary to a defect of the small middle ear bones1.

Skeletal manifestations are a common finding in STK-affected patients and they usually include the following:

  • Early-onset arthritis is common and may be severe is some cases, leading to the need for early surgical joint replacement1
  • Short stature relative to unaffected siblings. Short stature is present in all allelic disorders and sometimes might present important clinical feature for differential diagnosis.
  • Radiographic findings consistent with mild spondyloepiphyseal dysplasia, an inherited “bone growth disorder” manifested mostly by short stature and skeletal anomalies; based on abnormalities of the spine and the endings of the long bones (epiphyses).
  • Marfanoid body habitus (group of symptoms resembling Marfan syndrome, including long limbs, facial and joint abnormalities and others) but without tall stature5
  • Joint laxity that becomes less prominent with age1, 2
  • Abnormalities of the spine commonly include scoliosis, endplate abnormalities, kyphosis, and platyspondylia, all resulting in chronic back pain1, 6
  • Mitral valve prolapse has been reported in nearly 50% of individuals with Stickler syndrome1, 7 in one series and no individuals in another.

The incidence of Stickler syndrome among newborns can be estimated from data regarding the occurrence of Pierre Robin sequence in newborns; these data suggest that the incidence of Stickler syndrome among neonates is approximately 1:7,500-1:9,0001, 8.

Stickler syndrome is caused by mutations in one of collagen-associated genes, including COL2A1, COL9A1, COL9A2, COL11A1, and COL11A2 (Table 1).

Sequence analysis of exons 1-54 of COL2A1 and exons 14-67 of COL11A1 could identify approximately 90% of disease-causing mutations in STK-affected patients1, 12. The majority of individuals who have Stickler syndrome as a result of a COL2A1 pathogenic variant have premature stop (i.e., nonsense, frameshift, or splicing) mutations that result in functional haploinsufficiency of the COL2A1 product3, 1, 2.

Most affected individuals have type 1 congenital vitreous abnormalities with a high risk of retinal detachment, osteoarthritis and mild hearing loss14.

A large family with linkage to COL2A1 showed a unique p.Leu667Phe pathogenic variant producing a novel afibrillar vitreous gel abnormality3, 14. Furthermore, a COL2A1 missense mutation has been described in some families with characteristic ophthalmologic and craniofacial findings1.

Pathogenic variants involving exon 2 of COL2A1 are characterized by a predominantly ocular variant phenotype, in which individuals are at high risk of retinal detachment15. In the nine families with an exon 2 pathogenic variant of COL2A1, all pathogenic variants resulted in stop codons15.

Splicing and missense mutations and deletions in COL11A1 have been observed in individuals with the typical Stickler syndrome phenotype12, 13. Typically these individuals have more severe hearing loss and type 2 congenital vitreous anomalies or "beaded" vitreous phenotype1, 12, 13.

Pathogenic variants in COL11A2 have been shown to cause autosomal dominant non-ocular Stickler syndrome1, 13, while recessive pathogenic variants in COL9A1 have been shown to cause autosomal recessive Stickler syndrome (Stickler syndrome, type IV)9, 10. Affected individuals have moderate-to-severe sensorineural hearing loss, moderate-to-high myopia with vitreoretinopathy, cataracts, and epiphyseal dysplasia.


Overview of the genes in CENTOGENE´s Stickler syndrome panel

Gene
Protein
OMIM
chr. locus
Mutations frequency Allelic and associated disorders
(OMIM)
COL2A1

Collagen 2
Collagen of cartilage
Chondrocalcin
120140
12q13.11
80%-90%1, 12 Stickler syndrome, type I (108300); Stickler sydrome, type I, nonsyndromic ocular (609508); Spondyloperipheral dysplasia (271700); Spondyloepiphyseal dysplasia, Stanescu type (616583); Epiphyseal dysplasia with myopia and deafness (132450); Osteoarthritis with mild chondrodysplasia (604864); Otospondylomegaepiphyseal dysplasia (215150); Achondrogenesis, type II or hypochondrogenesis (200610); Avascular necrosis of the femoral head (608805); Czech dysplasia (609162), Kniest dysplasia (156550); Platyspondylic skeletal dysplasia, Torrance type (151210); SED congenita (183900) , SMED Strudwick type (184250) Legg-Calve-Perthes disease (150600)
COL9A1

Collagen 9
Casrtilage-specific short collagen
120210
6q13
Rare, few families 9, 10 Stickler syndrome, type IV (614134)
Multiple epiphyseal dysplasia 6 (614135)
COL9A2

Collagen 9A2
120260
1p34.2
Rare, 1 family11 Stickler syndrome, type V (614284)
Multiple epiphyseal dysplasia 2 (600204)
COL11A1

Collagen 11A1
120280
1p21.1
10%-20%1, 12 Stickler syndrome, type II (604841)
Marshall syndrome (154780)
Fibrochondrogenesis 1 (228520)
Lumbar disc herniation (603932)
COL11A2

Collagen 11A2
120290
6p21.32
Rare1, 13 Stickler syndrome, type III (184840);
Weissenbacher-Zweymuller syndrome (277610);
Otospondylomegaepiphyseal dysplasia (215150);
Fibrochondrogenesis 2 (614524);
Deafness, autosomal dominant 13 (601868);
Deafness, autosomal recessive 53 (609706)

There is no cure for Stickler syndrome. However, management in a comprehensive craniofacial clinic could be of great help for affected patients. Tracheostomy could be performed as needed in infants with Pierre Robin sequence. Mandibular advancement surgery could be performed in order to correct malocclusion for those with persistent micrognathia. Standard treatment of retinal detachment and sensorineural and conductive hearing loss and symptomatic treatment for arthropathy are recommended.

CENTOGENE offers the Stickler syndrome panel, including full gene sequencing (genes: COL2A1, COL9A1, COL9A2, COL11A1, COL11A2) and deletion/duplication analysis of selected genes (COL2A1, CO L11A1). In addition, any of the genes in the Stickler syndrome panel can also be ordered individually, for full gene sequencing and deletion/duplication analysis.


Differential diagnosis

The differential diagnosis of Stickler syndrome-related disorders – depending on the major symptoms in the initial case – includes the following diseases:

  • Wagner syndrome caused by mutations in the VCAN gene
  • VCAN-related vitreoretinopathy
  • High-grade myopia associated with mutations in one of the myopathy (NYP)-related loci
  • Nonsyndromic congenital retinal nonattachment (NCRNA)
  • Snowflake vitreoretinal degeneration
  • Binder syndrome (maxillonasal dysplasia)
  • Isolated Pierre Robin sequence or cleft/palate.

Testing strategy

CENTOGENE offers advanced, fast and cost-effective strategy to test large NGS panels and diagnose complex phenotypes based on the PCR-free Whole Genome Sequencing and NGS technology. This approach offers an unparalleled advantage by reducing amplification/capture biases and provides sequencing of entire gene at a more uniform coverage.

To confirm/establish the diagnosis, CENTOGENE offers the following testing strategy for Stickler syndrome using NGS Panel Genomic targeted towards this specific phenotype:

Step 1: Whole genome sequencing from a single filter card. The sequencing covers the entire genic region (coding region, exon/intron boundaries, intronic and promoter) for all the genes included in the Stickler syndrome panel. Copy Number Variants analysis derived from NGS data is also included.

Step 2: If no mutation is identified after analysis of the Stickler syndrome panel, based on the approval and consent, we further recommend to continue the bioinformatics analysis of the data obtained by whole genome sequencing to cover genes that are either implicated in an overlapping phenotype or could be involved in a similar pathway but not strongly clinically implicated based on the current information in literature.


Referral reasons

The following individuals are candidates for Stickler syndrome panel gene testing:

  • Individuals with a family history of Stickler syndrome and presentation of the most common symptoms such as: myopia, cataract, retinal detachment; hearing loss, midfacial underdevelopment and cleft palate
  • Individuals without a positive family history of Stickler syndrome, but with symptoms resembling this disease 
  • Individuals with a negative but suspected family history for Stickler syndrome, in order to perform proper genetic counseling (prenatal analyses are recommended in families with affected individuals).

Test utility

Sequencing, deletion/duplication of Stickler syndrome-related genes should be performed in all individuals suspected for Stickler syndrome. In parallel, other genes reported to be related with this clinical phenotype should also be analyzed for the presence of mutations, due to the overlap in many clinical features caused by those particular genes, mostly from the family of collagens-encoding and/or connective-tissue-associated genes.

Confirmation of a clinical diagnosis of Stickler syndrome through genetic testing can allow for genetic counseling and may direct medical management. Genetic counseling can provide a patient and/or family with the natural history of Stickler syndrome, to identify at-risk family members, provide reproductive risks as well as possible preventive therapy or preconception/prenatal options, and allow for appropriate referral for patient support and/or resources.


More information on CENTOGENE´s Stickler syndrome panel can be found in our genetic test catalogue.