What is Larsen syndrome

TL;DR: Larsen syndrome is a rare genetic disorder characterized by multiple joint dislocations, distinct facial features, and skeletal abnormalities such as clubfoot and scoliosis. It is caused by mutations in the FLNB gene and typically follows an autosomal dominant inheritance pattern, though recessive forms also exist.

What are the primary physical characteristics of Larsen syndrome?

Larsen syndrome affects the development of the skeletal system, leading to a unique set of clinical features. Individuals with Larsen syndrome often present at birth with "dislocations," particularly of the hips, knees, and elbows. The facial features associated with the condition are also highly characteristic; these include a prominent forehead, a depressed nasal bridge, and widely spaced eyes (hypertelorism). Because the condition involves the growth plates of the bones, patients frequently experience abnormal spinal curvature, such as scoliosis or kyphosis, and may have short stature. Other systemic issues can include respiratory complications due to a softened airway (tracheomalacia) and potential cardiovascular involvement.

What causes Larsen syndrome?

Larsen syndrome is primarily caused by mutations in the FLNB gene, which provides instructions for making a protein called filamin B. This protein is essential for the normal development of the skeleton and the formation of cartilage. When FLNB is mutated, the structural integrity of the joints and bones is compromised, leading to the instability and dislocations seen in those with Larsen syndrome. While the condition is most commonly inherited in an autosomal dominant manner (meaning only one copy of the mutated gene is needed to cause the disorder), there are rarer autosomal recessive forms of the condition that typically present with more severe skeletal involvement.

How common is Larsen syndrome and who is affected?

Larsen syndrome is considered an extremely rare disorder. While exact global prevalence numbers are difficult to establish due to potential under-diagnosis or misdiagnosis, it is estimated to affect fewer than 1 in 100,000 individuals worldwide. The condition affects both males and females equally, and there is no known geographic or ethnic predilection. Symptoms are usually identified at birth or in early infancy due to the obvious physical signs of joint dislocation and facial structure differences. On the DiseaseMaps.org platform, 58 people with Larsen syndrome have already joined our community to share their personal experiences and support one another.

What differentiates Larsen syndrome from other skeletal disorders?

It is important to distinguish Larsen syndrome from other conditions that involve joint laxity or skeletal dysplasia. Key diagnostic features that help clinicians differentiate this condition include:

• Multiple dislocations: The presence of congenital dislocations of the knees (often in hyperextension) and hips is a clinical hallmark.


• Foot abnormalities: Equinovarus (clubfoot) is frequently observed in infants with the condition.


• Cervical spine instability: A critical differentiator is the risk of spinal cord compression due to instability in the neck vertebrae, which requires careful monitoring.


• Distinctive craniofacial profile: The combination of a flat face and prominent forehead helps clinical geneticists narrow down the diagnosis.

Next steps

• Consult a clinical geneticist: A formal diagnosis should be confirmed through genetic testing to identify the specific FLNB mutation.


• Monitor spinal health: Establish a relationship with an orthopedic specialist who has experience in pediatric skeletal dysplasias to manage joint and spinal stability.


• Connect with the community: Join the 58 members at DiseaseMaps.org to share resources and find support from others navigating life with Larsen syndrome.


• Regular screenings: Discuss the need for regular cardiac and respiratory evaluations with your primary physician to ensure any secondary symptoms of Larsen syndrome are managed early.

Medical disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment; always seek the advice of your physician or other qualified health provider with any questions regarding a medical condition.

References

• NIH Genetic and Rare Diseases (GARD) Information Center: Larsen Syndrome Overview.


• Orphanet: The portal for rare diseases and orphan drugs (ORPHA:488).


• OMIM (Online Mendelian Inheritance in Man): Entry #150250 (Larsen Syndrome).


• National Library of Medicine (PubMed): Clinical literature on FLNB gene mutations.