Larsen Syndrome: Description And Symptoms
Larsen Syndrome is a rare, autosomal dominant, genetically heterogeneous disorder with a prevalence rate of one in every 100, 000 individuals born. Larsen syndrome is an osteochondrodysplasia, a medical term for developmental disorders of bone and cartilage,
that is characterized by big-joint dislocations and craniofacial abnormities.
The symptoms range from congenital dislocations of the joints (hip, knee, and elbow), club feet, scoliosis and cervical kyphosis, or spinal abnormalities, and the presence of short, broad, spatula-shaped distal phalanges of the thumbs. The craniofacial abnormities include: abnormally large forehead, flat nasal bridge and mid-face, and ocular hypertelorism.
A midline cleft palate, short stature, wide-spaced eyes and conductive loss of hearing is also presented in most cases. Foot deformities and the presence of supernumerary carpal and tarsal bones is another common symptom of Larsen Syndrome, especially during early childhood years.
What Causes Larsen Syndrome: The Genetic Aspects
Larsen syndrome is now known to be due to missense mutations or small in frame deletions in FLNB gene (filamin B, beta gene) which is located on chromosome 3, at the cytogenetic location “3p14.3". The gene FLNB encodes the cytoskeletal protein filamin B and mutations or deletions in it result in the severe bone and cartilage abnormalities in patients.
Larsen syndrome is genetically inherited as either an autosomal dominant or recessive type disorder. In the dominant type of inheritance, the child receives a single copy of the mutated FLNB gene from either parent and this copy of the gene is expressed in the dominant for causing manifestation of this disorder.
In the recessive type of inheritance, the disorder is not manifested if the child does not inherit mutated copies of the FLNB gene from both parents, but if both the copies of the FLNB gene inherited are mutated the child shows the disorder. When an individual gets one normal copy of the gene and one mutated copy of the gene, this person is a carrier of the gene but in most cases does not get the Larsen syndrome.
If a child is diagnosed with Larsen syndrome, then in order to assess the risk factors in subsequent pregnancies and for future sibling the parents can opt for genetic testing via a karyotype test. It is also a good idea to undergo genetic counseling to ascertain the risk factors. Prenatal testing in pregnancies which are at an increased risk for Larsen syndrome is possible, either via ultrasound) or if the disease-causing mutation in the family have been identified in genetic tests already.
Diagnosis, Treatment And Patient Management
The diagnosis is a step-wise process and is done through clinical and radiographic (X-ray) results initially and the facial abnormalities. It is confirmed by carrying out FLNB molecular genetic testing. This involves genetic tests like DNA analysis using linkage analysis, alignment sequencing or other procedures used in identifying mutations like karyotype tests. A karyotype test will reveal any abnormalities in the inherited chromosome 3.
The treatments used depend on the symptoms shown by the individual patient. All joint abnormalities need orthopedic treatments that may last a very long time. In infancy, spinal issues can be managed using posterior arthrodesis, myelopathic indications can be managed using both anterior decompression and circumferential arthrodesis. Joint defects such as dislocations can be treated using physiotherapy, specialized casts and braces and in serious cases corrective surgery. Patients with cleft palate can either use surgical interventions or opt for speech therapy. Respiratory issues (caused by flaccid cartilage) are common in Larsen syndrome and need treatment using physiotherapy or tracheotomy, and depending on the severity, the use of a ventilator.
The prognosis for the lifespan is till adulthood, with normal intelligence. Once a child has been diagnosed with Larsen syndrome for effective management, lateral cervical spine tests, audiometric testing and the extent of hip dislocation are essential to allow the proper choice of surgery procedures.
1) Bickell, S. L et al. (2007). A molecular and clinical study of Larsen syndrome caused by mutations in FLNB. Journal of Medical Genetics, 44:89–98. doi: 10.1136/jmg.2006.043687
2) ‘FLNB-Related Disorders.’ (2010). Retrieved on October 18th, 2010 from NCBI Bookshelf, GeneReviews: https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=flnb-dis#flnb-dis.Management
3) ‘MIM ID #150250 LARSEN SYNDROME, AUTOSOMAL DOMINANT; LRS1.’(2010). Retrieved on October 18th, 2010 from OMIM (Online Medelian Inheritance in Man), NCBI (National Center for Biotechnology Information, U.S. National Library of Medicine): https://www.ncbi.nlm.nih.gov/omim/150250
4) Becker, R. et al. (2000). Clinical variability of Larsen syndrome: diagnosis in a father after sonographic detection of a severely affected fetus. Clinical Genetics, 57: 148-150.