Overview
Acromesomelic dysplasia is a rare genetic disorder that mainly prevents normal bone growth. Thus, the person affected has a short stature as well as disproportionately short limbs. This disease makes the middle segment of the limbs, called “mesomelic”, and the distal segment, called “acromelic”, to be shorter. The proximal segments, on the other side, usually remain relatively normal. The genetic basis and inheritance patterns of acromesomelic dysplasia must be very well understood by patients and their families along with the healthcare providers to ensure that the disorder is managed adequately and that all the clinical implications are taken into consideration.
What is acromesomelic dysplasia?
Acromesomelic dysplasia is a type of skeletal dysplasia. In simpler words, this term refers to a group of disorders in which there is an abnormal development (dysplasia) of bones and cartilage (skeletal). Those suffering from acromesomelic dysplasia usually have significantly shortened limbs, especially in the forearms and lower legs. It is important to mention that usually the upper body (upper arms and thighs) are less affected. This disproportionate growth pattern is responsible for creating a distinct physical appearance, which in many cases can be associated with other health issues, including joint problems and in some cases can cause delays in development.1
Looking at the etymology of the term "acromesomelic" it can be observed that it is derived from Greek, from the words "akron" (=extremity) and "mesos" (=middle). This reflects the involvement of the distal and middle segments of the limbs. Acromesomelic dysplasia can be classified into many subtypes, each representative of a specific genetic mutation that disrupts normal bone development.
Genetic basis of acromesomelic dysplasia
The genetic basis of acromesomelic dysplasia involves mutations in specific genes that play an important role in bone growth and development. Each subtype of acromesomelic dysplasia can be correlated with a mutation in a specific gene:
Acromesomelic dysplasia, maroteaux type (AMDM)
A mutation in the NPR2 gene is responsible for this type of acromesomelic dysplasia. The NPR2 gene provides instructions for making a protein called natriuretic peptide receptor B (NPR-B), which plays a critical role in signalling pathways that promote bone growth and development.2 Mutations in NPR2 disrupt these pathways, leading to the characteristic skeletal abnormalities seen in AMDM.
Acromesomelic dysplasia, hunter-thompson type
This subtype results from mutations in the GDF5 gene. The GDF5 gene encodes a protein that is involved in the formation and maintenance of cartilage and bones. Mutations in GDF5 disrupt these processes, leading to the skeletal features characteristic of this subtype.3
Acromesomelic dysplasia, grebe type
This type also involves mutations in the GDF5 gene, similar to the Hunter-Thompson type, but it tends to present more severe skeletal abnormalities.4 The differences in severity between these subtypes may be due to the specific nature and location of the mutations within the GDF5 gene.
The genes presented above are essential for normal skeletal development. When mutations occur this leads to a disrupted formation and growth of bones, resulting in the characteristic features of acromesomelic dysplasia.
Inheritance patterns
Acromesomelic dysplasia is a condition that follows a pattern called autosomal recessive inheritance. This means that to have the disorder, a person needs to get two copies of the faulty gene – one from each parent. In general, the parents of someone affected by this disease are carriers. This means they each carry one copy of the mutated gene but don't show any symptoms themselves because they also have one normal gene to balance things out.
When both parents are carriers, here's how it breaks down for each pregnancy:
- There's a 25% chance the child will inherit both mutated genes (one from each parent) and will have acromesomelic dysplasia
- There's a 50% chance the child will get one mutated gene and one normal gene. In this case, the child will be a carrier just like the parents but won't have the disorder
- Finally, there's a 25% chance the child will inherit two normal genes, meaning they won't have the disorder and won't be a carrier either
Because of this autosomal recessive pattern, the disorder can sometimes show up out of the blue in families with no previous history, especially when the parents don't know they're carriers.
This is why genetic counselling is super important for families dealing with acromesomelic dysplasia. It helps them understand the inheritance pattern, figure out the risks for future kids, and grasp what this means for other family members.6
Diagnosis and management
Acromesomelic dysplasia is diagnosed using a combination of clinical evaluation, family history, and genetic testing. The physical examination should reveal the expected specific skeletal abnormalities associated with this disorder. Then, through the means of radiographic imaging, the bone growth and structure can be assessed. Ultimately, genetic testing is used to confirm the diagnosis by identifying mutations in the relevant genes.7
During clinical evaluation, the limb segments are measured to assess the disproportionate shortening. Furthermore, a detailed family history is made to identify any patterns that might suggest a hereditary condition. Radiographs or X-rays are crucial because they enable the healthcare provider to observe the specific bone deformities that are indicative of acromesomelic dysplasia.
Management of acromesomelic dysplasia is multidisciplinary. It is mainly focused on addressing the symptoms and complications associated with the condition. Key aspects of management include:
- Orthopaedic care: The treatment used to treat the various bone and joint issues that can occur must be constantly monitored. In some cases, surgical interventions can be necessary to correct severe deformities or to improve function and mobility. Orthopaedic care often involves procedures that can help address discrepancies in limb length, joint deformities, and other skeletal issues that can affect the patient’s mobility and as a result their quality of life
- Physical therapy: Physical therapy is an important aspect of the treatment as it can help enhance mobility and strength, improve posture, and reduce the risk of joint contractures. Personalized physical therapy programs are essential in managing this disorder. These programmes are designed to meet the specific needs of each patient as they focus on maintaining flexibility, strengthening muscles, and overall promoting functional independence
- Genetic counselling: Genetic counselling is a crucial aspect for both affected individuals and their families. Thai counselling can help them develop a good understanding of the inheritance pattern, the risks of recurrence in future pregnancies, and the implications for other family members. Genetic counsellors provide information on the genetic aspects of the disorder, discuss potential testing options for family members, and offer support in decision-making regarding family planning5
Living with acromesomelic dysplasia
Living with acromesomelic dysplasia can pose significant challenges due to physical limitations and potential health issues. However, despite these, appropriate medical care, support, and adaptive strategies can enable individuals with this condition to live a relatively normal life.
In the past few years, various adaptive devices and modifications have been developed to assist with daily activities and improve independence. For example, specialised equipment such as customized seating, mobility aids, and ergonomic tools can help individuals perform tasks more easily and comfortably.
Additionally, home modifications such as ramps, widened doorways, and adjusted counter heights can have a huge impact on a patient’s life as they improve accessibility and safety.
Psychological support and community resources are also important for addressing the social and emotional aspects of living with a rare genetic disorder. Support groups, counselling services, and educational programs can provide valuable resources and connect individuals with others who share similar experiences.
Current research and future directions
Research on acromesomelic dysplasia is ongoing, with scientists aiming to better understand the underlying genetic mechanisms and develop potential therapies. Advances in genetic technologies, such as gene editing and targeted molecular therapies, hold promise for the future treatment of genetic disorders like acromesomelic dysplasia.8
Studies are also exploring the broader implications of gene mutations involved in acromesomelic dysplasia, which may provide insights into other skeletal disorders and general bone biology. For example, research into the NPR2 and GDF5 genes can enhance our understanding of skeletal development and potentially lead to new treatments for a range of bone-related conditions.
Gene therapy is an area of particular interest, as it involves correcting or replacing defective genes to treat genetic disorders. While still in the experimental stages, gene therapy has shown promise in preclinical studies and could offer a future treatment option for acromesomelic dysplasia and other genetic conditions.8
Another area of research focuses on developing pharmacological treatments that can modulate the signalling pathways involved in bone growth and development. For example, researchers are investigating drugs that can enhance the activity of natriuretic peptide receptor B or promote the function of growth differentiation factor 5, potentially offering therapeutic benefits for individuals with acromesomelic dysplasia.
Summary
Acromesomelic dysplasia is a rare genetic disorder with distinct skeletal abnormalities resulting from mutations in specific genes. Understanding its genetic basis and inheritance patterns is crucial for diagnosis, management, and genetic counselling.
While living with acromesomelic dysplasia can be challenging, advancements in medical care and ongoing research offer hope for improved treatments and quality of life for affected individuals.
The support of multidisciplinary care teams, adaptive strategies, and community resources can help individuals with acromesomelic dysplasia navigate the challenges of the condition and lead fulfilling lives.
As research continues to advance, there is optimism that new therapies and treatments will emerge, providing even greater support and options for those affected by this rare disorder.
References
- Maroteaux P, Stanescu R, Stanescu V. Acromesomelic dysplasia: a new description. Rev Rhum Mal Osteoartic. 1971;38(10):797-805.
- Bartels CF, Bükülmez H, Padayatti P, et al. Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux. Am J Hum Genet. 2004;75(1):27-34.
- Thomas JT, Lin K, Nandedkar M, et al. A human chondrodysplasia due to a mutation in a TGF-beta superfamily member. Nat Genet. 1996;12(3):315-317.
- Polinkovsky A, Robin NH, Thomas JT, et al. Mutations in CDMP1 cause autosomal dominant brachydactyly type C and autosomal recessive acromesomelic chondrodysplasia. Nat Genet. 1997;17(1):121-122.
- OMIM. Online Mendelian Inheritance in Man. Johns Hopkins University. Acromesomelic Dysplasia, Maroteaux Type; AMDM. Available from: https://www.omim.org/entry/602875.
- Bieganski T, Jamsheer A, Sowinska-Seidler A, et al. A family-based approach significantly increases efficiency of homozygosity mapping in autosomal recessive acromesomelic dysplasia. Clin Genet. 2014;86(3):258-264.
- Savarirayan R, Rimoin DL. The skeletal dysplasias. Best Pract Res Clin Endocrinol Metab. 2002;16(3):547-560.
- Bayat A, McGrouther DA. Gene therapy for disorders of the musculoskeletal system: current developments. BMJ. 2006;332(7533):1163-1167.
