Larsen syndrome

Larsen syndrome is a disorder in which bones and joints do not form in the usual way before birth. NORD describes it as a rare condition affecting skeletal development and joint function, occurring in approximately 1 in 100,000 people.

The classic form is autosomal dominant and results from mutations in the FLNB gene. NORD explains that the gene encodes filamin B, and faults in it disrupt vertebral segmentation, joint formation and the building of the skeleton. The change can be inherited from a parent or can appear for the first time in the affected child.

The most striking finding in a newborn is that several large joints are out of their sockets. NORD gives figures for how often particular findings occur in the people it describes, which help show the pattern.

• Widely spaced eyes and a flattened or depressed nasal bridge.

• Possible hearing loss.

• Possible breathing difficulties, particularly in infancy.

Diagnosis usually rests on the combination of dislocated joints, foot deformity and facial features, supported by X-rays. A genetic test can look for a change in FLNB. Because other conditions also cause joint dislocations at birth, a clinical geneticist is often involved to separate Larsen syndrome from related disorders, including some forms of Ehlers-Danlos syndrome and other skeletal dysplasias.

Imaging of the neck is a priority because instability or abnormal alignment of the cervical vertebrae can put the spinal cord at risk, especially if an anaesthetic is planned.

NORD states that management is individualised and typically involves joint manipulation, corrective casts, physical therapy and orthopaedic surgery when necessary. Early treatment of the feet with serial casts and sometimes surgery aims for a foot that can bear weight in a shoe. Hip and knee dislocations are often corrected surgically in infancy or early childhood, with timing decided by the orthopaedic team.

Cervical spine stabilisation may be needed because of the risk of damage to the spinal cord. A multidisciplinary team that includes orthopaedic surgeons, a geneticist and other specialists coordinates care. In the UK, children with suspected skeletal dysplasia are usually referred through a paediatrician to regional specialist orthopaedic and genetics services.

Physiotherapy and occupational therapy help build strength around corrected joints, support walking and school participation and provide equipment where needed. Hearing and breathing are checked regularly, and spinal curvature is monitored during growth with bracing or surgery considered if it progresses.

Anaesthetic teams should know about the diagnosis before any procedure so that neck positioning and airway management are planned. Families may find it useful to carry a summary letter that states the neck findings and any airway issues.

NORD describes Larsen syndrome as lifelong but notes that early intervention and comprehensive management help to optimise function and quality of life. Outcomes depend on how many joints are involved, how the spine behaves and whether breathing is affected in infancy.

An affected person with the dominant form has a 50% chance of passing the gene change to each child, while a new change in a child with unaffected parents carries a low chance of recurrence, though a genetics service can advise on the individual situation. Seek urgent help for new weakness or numbness in the arms or legs, loss of bladder or bowel control, severe neck pain after a fall, or noisy or laboured breathing, using 999 where symptoms are sudden or severe.