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Distal arthrogryposis
These conditions primarily cause stiff joints in the hands and feet, which can impact mobility and daily activities. They are typically present at birth and vary in severity, affecting individuals differently.
Overview
Distal arthrogryposis (DA) describes a group of rare genetic conditions primarily characterised by multiple joint contractures present at birth. 'Contracture' means the joint is fixed in a bent or straightened position, limiting its range of motion. Unlike some other forms of arthrogryposis, DA typically affects joints in the extremities - specifically the hands and feet - more severely than the larger joints like knees or hips [PMID:24127042].
There are several types of distal arthrogryposis, each with slightly different features, although they all share the common characteristic of contractures in the 'distal' (further away from the body's centre) joints. The severity can range from mild, involving only a few joints, to more severe, impacting a wider range of joint movement. Despite the joint issues, muscle weakness is usually not a primary feature, and cognitive development is typically unaffected.
Symptoms & clinical features
The main symptom of distal arthrogryposis is the presence of joint contractures at birth. These commonly include clenched fists, overlapping fingers, and feet that are turned inwards or outwards (clubfoot or talipes equinovarus) [PMID:24127042]. The hands may show small, fixed joints, often with the thumbs tucked into the palm.
Foot abnormalities are also common, with feet sometimes described as 'rocker-bottom' or having other unusual shapes that affect walking. While the hands and feet are most commonly and severely affected, other joints such as the elbows, shoulders, hips, and knees may occasionally show milder contractures. The degree to which these contractures impact movement can vary significantly between individuals.
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Affected organs
Distal arthrogryposis primarily affects the musculoskeletal system, specifically the joints of the extremities. The most significantly affected body parts are generally the hands and feet, where multiple joints can be fixed in position. Muscles and connective tissues around these joints may also be secondarily affected due to the contractures.
While the condition is mainly confined to the skeletal system, some forms of distal arthrogryposis may rarely be associated with other features, such as short stature or mild facial differences. However, significant organ involvement or neurological issues are not typical features of most types of distal arthrogryposis.
Risks & severity
The severity of distal arthrogryposis can vary widely, even within the same type. Some individuals may have only mild contractures that have minimal impact on daily life, while others may experience more significant limitations in joint movement, requiring ongoing management. The condition is present from birth, so the effects on joint mobility are lifelong.
Distal arthrogryposis is considered a rare condition, though exact prevalence figures are not well established for all types. The long-term outlook often depends on the specific genetic cause and the availability of early intervention and ongoing therapies to improve joint function. Life expectancy is generally not affected by distal arthrogryposis itself, unless there are rare, severe associated features.
Genetic causes
Distal arthrogryposis is caused by changes (variants) in specific genes that play a role in muscle development and joint movement. These gene changes can disrupt the normal formation or function of proteins essential for muscle contraction or connective tissue integrity, leading to joint contractures. Identified causative genes include MYH3, PIEZO2, and TNNI2.
Variants in MYH3 (myosin heavy chain 3) are associated with several types of distal arthrogryposis [PMID:27848074]. MYH3 provides instructions for making a protein critical for muscle contraction. Alterations can affect the ability of muscles to develop or function correctly, leading to stiff joints.
PIEZO2 (piezo type mechanosensitive ion channel component 2) produces a protein involved in sensing touch and body position. Changes in PIEZO2 can affect proprioception (the body's sense of its own position in space), which may contribute to joint contractures. Variants in TNNI2 (troponin I2, fast skeletal type) affect a protein that helps regulate muscle contraction, and disruptions can lead to rigid joints.
- MYH3 myosin heavy chain 3
- PIEZO2 piezo type mechanosensitive ion channel component 2
- TNNI2 troponin I2, fast skeletal type
Inheritance pattern
Distal arthrogryposis can be inherited in different ways, most commonly autosomal dominant or autosomal recessive. In an autosomal dominant pattern, a person only needs to inherit one copy of the altered gene from one parent to develop the condition. This means there is a 50% chance for each child of an affected parent to inherit the condition.
In an autosomal recessive pattern, a person must inherit two copies of the altered gene - one from each parent - to be affected. If both parents are carriers (meaning they each have one altered copy but do not show symptoms), there is a 25% chance with each pregnancy for their child to inherit two altered copies and develop the condition. Family members may wish to seek genetic counselling to understand the specific inheritance pattern for their family and the risks for future children.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
Diagnosis & testing
The diagnosis of distal arthrogryposis is often suspected at birth based on the presence of characteristic joint contractures. A clinical geneticist or paediatrician will typically perform a thorough physical examination to assess the range and severity of joint involvement. They may also ask about family history to look for patterns of inheritance.
To confirm the diagnosis and identify the specific type, genetic testing is usually performed. This involves analysing a blood sample to look for variants in genes known to cause distal arthrogryposis, such as MYH3, PIEZO2, and TNNI2. Genetic testing for arthrogryposis is available on the NHS Genomic Medicine Service through specific R-codes, such as R89 or R83, which allow clinicians to order comprehensive gene panels to identify the underlying genetic cause. Referral to a clinical genetics service is essential for appropriate testing and interpretation of results.
Management & lifestyle
Management for individuals with distal arthrogryposis focuses on improving joint mobility and function, and it is tailored to the specific needs of each person. This often involves a multidisciplinary team including orthopaedic specialists, physiotherapists, and occupational therapists. Physiotherapy is crucial from an early age to stretch contracted joints and strengthen muscles.
Occupational therapy can help individuals adapt to daily tasks and suggest assistive devices if needed. Splinting, casting, and orthoses (braces) may be used to gently stretch joints and maintain improved positions. In some cases, surgical interventions may be considered to release severe contractures or correct skeletal deformities. Ongoing monitoring and support within the NHS care pathway, including regular appointments with specialists, are vital for managing the condition throughout life.
UK care pathway
In the UK, individuals with suspected distal arthrogryposis typically enter the NHS Genomic Medicine Service pathway. This journey often begins with a referral from a GP or paediatrician to a clinical genetics service. Genetic counsellors play a key role, offering support and information to families, explaining inheritance patterns, and helping navigate the diagnostic process.
Genetic testing, guided by NHS National Genomic Test Directory R-codes (e.g., R89 for arthrogryposis cases with a Mendelian inheritance pattern), allows for a precise diagnosis. Once a genetic cause is identified, the clinical team can provide more accurate information about the prognosis and guide management strategies, connecting patients with relevant specialists for ongoing care and support.
Frequently asked questions
Will my child's distal arthrogryposis get worse over time?
Distal arthrogryposis is present from birth, meaning the joint contractures are typically evident at a very young age. The condition usually does not worsen significantly over time, but the impact on function can change as a child grows. Early and ongoing therapy can often improve joint mobility and function.
Is distal arthrogryposis always inherited from my parents?
Not always. While distal arthrogryposis can be inherited in autosomal dominant or autosomal recessive patterns, some cases can arise from a new (de novo) genetic variant in the affected individual, meaning it wasn't inherited from either parent. Genetic counselling can help determine the specific inheritance pattern in your family.
Can physiotherapy help with distal arthrogryposis?
Yes, physiotherapy is a cornerstone of managing distal arthrogryposis. Starting early and continuing with regular therapy can help to gently stretch contracted joints, improve range of motion, and strengthen surrounding muscles. Occupational therapy also plays a key role in adapting daily activities.
Are there any specific medical treatments for distal arthrogryposis?
There isn't a specific drug treatment that cures distal arthrogryposis, as it's caused by genetic changes. Management focuses on physical therapies, casting, splinting, and sometimes surgery to improve joint function. The aim is to maximise an individual's mobility and independence.
Will having distal arthrogryposis affect my child's learning or intelligence?
Typically, distal arthrogryposis primarily affects the physical musculoskeletal system. Most individuals with distal arthrogryposis have normal cognitive development and intelligence. If there are learning difficulties, they would usually be due to another, unrelated cause.
References
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