Larsen syndrome is a rare genetic disorder of connective tissue that causes dislocations of multiple large joints at birth, distinctive facial features, and skeletal abnormalities, particularly in the spine. It affects roughly 1 in 100,000 to 200,000 newborns and stems most often from mutations in the FLNB gene, which encodes a protein critical to cartilage and bone development.1PubMed Central. Larsen Syndrome and Associated Spinal Deformities While the joint dislocations are the hallmark that typically leads to a diagnosis, the condition’s reach extends well beyond the skeleton, involving the airway, heart, and hearing in ways that can shape a child’s medical care for years.
What Larsen Syndrome Looks Like at Birth
The most immediately obvious sign is that a newborn’s knees, hips, or elbows are visibly dislocated. Knee dislocations tend to be the most dramatic and are often the first thing noticed in the delivery room. The legs may be hyperextended or bent backward, a finding called genu recurvatum. Hips are frequently dislocated bilaterally, and the elbows can be partially or fully out of joint. Clubfoot deformities are also common.
Facial features follow a recognizable pattern: a flattened midface, a depressed nasal bridge, and wide-set eyes. These features alone are not diagnostic but in combination with the joint findings they create a clinical picture that experienced clinicians recognize.2PubMed Central. A Further Case of Larsen’s Syndrome: Clinical and Genotypic Challenges in Diagnosis The hands often show distinctive findings too: short, broad fingertips with a spatula-like appearance, and the wrists may contain extra carpal bones, a feature unusual enough that it can serve as a radiographic clue.3PubMed Central. Images – Extra (too many) carpal bones in Larsen’s syndrome One study reviewing the literature noted that supernumerary carpal bones are among the hand anomalies commonly associated with the syndrome.4Plastic Surgery Case Studies. Supernumerary Carpal Bones in Larsen Syndrome: A Review of the Literature and Case Study
A study of seven patients found that while all exhibited the typical facial features and joint dislocations, the carpal bone picture was not always what textbooks describe. Contrary to the widely reported advanced carpal ossification, two of those patients actually showed delayed ossification, a reminder that individual variation exists even within a well-characterized syndrome.5PubMed Central. Phenotype and genotype in patients with Larsen syndrome: clinical homogeneity and allelic heterogeneity in seven patients
The Genetic Roots
The most common form of Larsen syndrome follows an autosomal dominant inheritance pattern, meaning a single copy of the mutated gene is enough to cause the condition. The responsible gene is FLNB, which codes for filamin B, a protein that acts as a kind of scaffold inside cells. Filamin B cross-links actin filaments, connects the cell membrane to the internal cytoskeleton, and helps regulate signaling pathways that guide how cartilage and bone develop.6PubMed. Filamin B mutations cause chondrocyte defects in skeletal development
The mutations are not scattered randomly across the gene. They cluster in specific regions, particularly in the part of the protein that binds actin and in a stretch known as filamin repeats 13 through 17. All Larsen-associated FLNB mutations identified so far are either missense changes (a single amino acid swap) or small in-frame deletions, meaning the protein is still produced but functions abnormally rather than being absent entirely.7PubMed Central. A molecular and clinical study of Larsen syndrome caused by mutations in FLNB This distinction matters because complete loss of filamin B causes a different and generally more severe skeletal condition called spondylocarpotarsal syndrome, which involves premature vertebral fusions and short stature.8PubMed Central. Filamin B regulates chondrocyte proliferation and differentiation through Cdk1 signaling
Many cases arise from new (de novo) mutations, meaning neither parent carries the mutation in their own cells. However, parental gonadal mosaicism can complicate genetic counseling. In one documented case, a father with Larsen syndrome was found to carry his FLNB mutation in only about 7 to 10 percent of the cells tested across different tissues, including roughly 7 percent of sperm cells. That low-level mosaicism meant the mutation was present in his germ line and could be passed to offspring, even though he appeared only mildly affected.9PubMed Central. Quantification of transmission risk in a male patient with a FLNB mosaic mutation causing Larsen syndrome
The Recessive Form and Related Conditions
Not all Larsen syndrome is autosomal dominant. A rarer recessive form exists, caused by mutations in the CHST3 gene, which encodes an enzyme involved in building cartilage’s structural sugar chains. Patients with this form tend to have severe joint dislocations and progressive spinal degeneration. In older patients studied with CHST3 mutations, all needed crutches or a wheelchair for mobility, and their spinal imaging showed marked disk degeneration and thoracic kyphosis.10American Journal of Human Genetics. Congenital Joint Dislocations Caused by Carbohydrate Sulfotransferase 3 Deficiency in Recessive Larsen Syndrome and Humero-Spinal Dysostosis
Adding further complexity, mutations in B3GAT3, another gene involved in building sugar-chain scaffolds on proteins, cause a Larsen-like phenotype sometimes called a “linkeropathy.” The clinical overlap can make diagnosis tricky. In one Indonesian family, researchers found a novel B3GAT3 mutation causing a skeletal dysplasia that shared features with Larsen syndrome but lacked the heart involvement seen in other B3GAT3 mutations.11PubMed. Skeletal dysplasia in a consanguineous clan from the island of Nias/Indonesia is caused by a novel mutation in B3GAT3 Separate case reports have continued to expand the spectrum of B3GAT3-related disorders, reinforcing that genetic testing is often necessary to sort out what’s causing the clinical picture.12PubMed Central. The clinical and mutational spectrum of B3GAT3 linkeropathy: two case reports and literature review
Why the Cervical Spine Is the Biggest Concern
If there is one part of Larsen syndrome that keeps clinicians up at night, it is the cervical spine. The vertebrae in the neck can be underdeveloped, abnormally shaped, or poorly segmented. When the vertebral bodies at the C4 or C5 level are markedly hypoplastic, the neck curves forward instead of maintaining its normal gentle backward curve, a deformity called cervical kyphosis. This puts the spinal cord at risk of compression.13Spine Deformity. Review of Cervical Kyphosis in Larsen Syndrome
Cervical kyphosis occurs in roughly 12 percent of people with Larsen syndrome, and myelopathy, the progressive loss of spinal cord function caused by compression, develops in close to 15 percent.14PubMed Central. Larsen Syndrome and Associated Spinal Deformities The consequences of myelopathy range from distal muscle weakness and wasting to complete quadriplegia. Instability at the junction between the first and second cervical vertebrae (C1-C2) is another recognized problem, potentially causing symptomatic spinal cord compression even without an obvious kyphotic curve.15PubMed Central. Craniovertebral junction instability in Larsen syndrome: An institutional series and review of literature
The deformity tends to worsen over time, and late diagnosis is associated with more severe curvature and worse neurological outcomes.16Spine Deformity. Review of Cervical Kyphosis in Larsen Syndrome This is why experts recommend that every child diagnosed with Larsen syndrome get cervical spine X-rays at the first clinical visit. If the kyphosis is mild and the spine is still flexible, a posterior spinal fusion (fusing the bones from behind) can stabilize things and allow the front of the vertebrae to continue growing, gradually correcting the curve. When the kyphosis is severe or structural and the child already shows signs of myelopathy, the surgical approach is more aggressive: anterior decompression to relieve pressure on the cord, combined with fusion from both front and back.17Spine. Surgical Treatment of Cervical Kyphosis in Larsen Syndrome
Airway Problems
The same connective-tissue weakness that destabilizes joints can soften the cartilage rings that hold the windpipe open. Tracheomalacia, a floppy trachea that tends to collapse during breathing, has been reported in children with Larsen syndrome and can manifest as stridor (a high-pitched breathing sound), cyanosis (bluish skin from low oxygen), apnea, and recurrent pneumonias. In at least one reported case, the softening extended into the bronchi as well, producing diffuse bronchomalacia.18PubMed. Tracheomalacia and bronchomalacia associated with Larsen syndrome
These airway complications are important to recognize early because they can complicate anesthesia and surgical planning. A child who needs repeated orthopedic procedures, as many with Larsen syndrome do, faces compounded risk if the anesthesia team is unaware of a floppy airway.
Heart and Hearing Involvement
Larsen syndrome can affect the cardiovascular system in ways that echo what is seen in Marfan syndrome. Aortic root dilation, mitral valve prolapse, and other structural heart findings have been documented. One early case series noted that the aortic lesions in Larsen patients may carry the same prognostic weight as those in Marfan syndrome, prompting the recommendation that every patient with Larsen syndrome undergo thorough cardiac evaluation.19PubMed. Cardiovascular manifestations in the Larsen syndrome A more recent case report described a five-year-old girl with severe aortic root dilation who required surgical intervention, underscoring that these cardiac findings can be clinically significant even in young children.20PubMed. Severe Aortic Root Dilatation in a Patient With Larsen Syndrome
Hearing loss is another underappreciated feature. A review of the literature identified seven studies reporting hearing loss in Larsen syndrome patients. Four of those cases involved conductive hearing loss, meaning sound was not being transmitted properly through the middle ear, and three involved a mixed pattern combining conductive and sensorineural components. Possible causes include malformed ossicles (the tiny bones of the middle ear), middle ear fluid, Eustachian tube dysfunction, and cleft palate, which occurs in some patients and can further interfere with middle ear drainage.21PubMed. Otologic manifestations of Larsen syndrome Because untreated hearing loss in young children directly impairs speech and language development, audiology screening should be part of routine follow-up.
Orthopedic Management and Timing
Children with Larsen syndrome often face a series of surgical procedures spread over the first several years of life, and the question of what to treat first is not straightforward. One detailed case report laid out a practical approach: the team used Ponseti casting (a method originally designed for clubfoot) to address both the foot deformities and knee dislocations simultaneously in the early months of life. When a knee failed to reduce with casting alone, they performed an open reduction at four months. Hip dislocations were addressed surgically at eight months. A clubfoot that relapsed later required additional surgery at two years.22PubMed Central. Management of joint dislocations of the lower limb in Larsen syndrome: practical approach
The general principle is to begin with the lower-limb deformities that interfere most with future mobility, typically the knees and feet, and move on to hips once those are stabilized. Each subsequent procedure is guided by how the child is developing functionally rather than following a rigid protocol. Because the joints in Larsen syndrome tend to be inherently lax, achieving stable surgical reductions can be more difficult than in a child with an isolated congenital dislocation, and re-operations are not uncommon.
Long-term follow-up data from families with recessive Larsen syndrome (CHST3 mutations) illustrate the range of outcomes. In that cohort, all older patients required mobility aids, and spinal degeneration was progressive.23American Journal of Human Genetics. Congenital Joint Dislocations Caused by Carbohydrate Sulfotransferase 3 Deficiency in Recessive Larsen Syndrome and Humero-Spinal Dysostosis By contrast, a long-term follow-up of two siblings with the dominant form found that with careful orthopedic management, the prognosis could be good despite severe initial deformities.24PubMed. Long-term follow-up of two sibs with Larsen syndrome possibly due to parental germ-line mosaicism The underlying genetic form seems to play a significant role in long-term trajectory.
Prenatal Detection
Larsen syndrome can sometimes be spotted before birth. Bilateral genu recurvatum, the backward bending of both knees, is a striking ultrasound finding that can prompt further investigation. In one reported case, three-dimensional ultrasound identified the knee abnormality and subsequently revealed the characteristic facial features, leading to a prenatal diagnosis.25PubMed. Three-dimensional ultrasound diagnosis of Larsen syndrome with further characterization of neurological sequelae
A systematic review of fetal congenital knee dislocation recommended that when this finding is not isolated, meaning other anomalies are present, prenatal workup should include detailed ultrasound assessment and amniocentesis for genetic testing.26PubMed. Prenatal diagnosis and postnatal outcome of fetal congenital knee dislocation: systematic review of literature Prenatal diagnosis does not change the course of the pregnancy in most cases, but it gives the medical team time to plan delivery at a center equipped for the neonatal care the child will need, including cervical spine precautions and airway management.
Anesthetic Risks That Families Should Know About
Because children with Larsen syndrome often undergo multiple surgeries, anesthesia becomes a recurring concern. The combination of a potentially difficult airway (from midface hypoplasia and sometimes a floppy trachea), an unstable cervical spine, and poor pulmonary reserve from chest wall deformities creates a situation that demands careful planning. Intubation requires extreme caution to avoid extending or flexing the neck in ways that could damage the spinal cord. Abnormal posturing from spinal deformities can complicate patient positioning on the operating table. And kyphoscoliosis can reduce lung capacity, making ventilation trickier than in a child with a normal chest.27PubMed Central. Anesthetic challenges in the management of Larsen syndrome: A rare congenital anomaly
For families, the practical takeaway is to make sure the anesthesia team is informed about the diagnosis well before any scheduled procedure. Ideally, anesthesia for a child with Larsen syndrome should be managed at a center with pediatric anesthesiologists experienced in handling airway and spinal challenges. This applies not just to orthopedic surgeries but to any procedure requiring general anesthesia, including dental work or ear tube placement.
Getting to a Diagnosis
Diagnosis often begins clinically, with the combination of multiple joint dislocations, distinctive facial features, and characteristic hand findings raising suspicion. Imaging plays a supporting role: X-rays of the wrists may reveal supernumerary carpal bones,28PubMed Central. Images – Extra (too many) carpal bones in Larsen’s syndrome and cervical spine films may show vertebral hypoplasia or kyphosis. But genetic testing is what confirms the diagnosis. In one case, a five-month-old boy presenting with the cardinal triad of large-joint dislocations, digit anomalies, and craniofacial dysmorphism had his diagnosis confirmed by exome sequencing, which identified a novel missense variant in FLNB.29PubMed Central. A Further Case of Larsen’s Syndrome: Clinical and Genotypic Challenges in Diagnosis
Genetic confirmation is especially valuable because it can distinguish dominant from recessive forms, guide prognosis, and inform genetic counseling for future pregnancies. As the spectrum of FLNB-related and linkeropathy-related conditions has grown, clinical features alone are no longer enough to pin down the exact genetic cause, and families benefit from knowing which gene is involved. A child with dominant Larsen syndrome from an FLNB missense mutation faces a different trajectory than a child with recessive Larsen syndrome from CHST3 mutations, where progressive spinal degeneration tends to be more relentless.