Atelosteogenesis type 1

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Atelosteogenesis type 1 is a disorder that affects the development of bones throughout the body. Affected individuals are born with inward- and upward-turning feet (clubfeet) and dislocations of the hips, knees, and elbows. Bones in the spine, rib cage, pelvis, and limbs may be underdeveloped or in some cases absent. As a result of the limb bone abnormalities, individuals with this condition have very short arms and legs. Characteristic facial features include a prominent forehead, wide-set eyes (hypertelorism), an upturned nose with a grooved tip, and a very small lower jaw and chin (micrognathia). Affected individuals may also have an opening in the roof of the mouth (a cleft palate). Males with this condition can have undescended testes.

Individuals with atelosteogenesis type 1 typically have an underdeveloped rib cage that affects the development and functioning of the lungs. As a result, affected individuals are usually stillborn or die shortly after birth from respiratory failure.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the FLNB gene cause atelosteogenesis type 1. The FLNB gene provides instructions for making a protein called filamin B. This protein helps build the network of protein filaments (cytoskeleton) that gives structure to cells and allows them to change shape and move. Filamin B attaches (binds) to another protein called actin and helps the actin to form the branching network of filaments that makes up the cytoskeleton. Filamin B also links actin to many other proteins to perform various functions within the cell, including the cell signaling that helps determine how the cytoskeleton will change as tissues grow and take shape during development.

Filamin B is especially important in the development of the skeleton before birth. It is active (expressed) in the cell membranes of cartilage-forming cells (chondrocytes). Cartilage is a tough, flexible tissue that makes up much of the skeleton during early development. Most cartilage is later converted to bone, a process called ossification, except for the cartilage that continues to cover and protect the ends of bones and is present in the nose, airways (trachea and bronchi), and external ears. Filamin B appears to be important for normal cell growth and division (proliferation) and maturation (differentiation) of chondrocytes and for the ossification of cartilage.

FLNB gene mutations that cause atelosteogenesis type 1 change single protein building blocks (amino acids) in the filamin B protein or delete a small section of the protein sequence, resulting in an abnormal protein. This abnormal protein appears to have a new, atypical function that interferes with the proliferation or differentiation of chondrocytes, impairing ossification and leading to the signs and symptoms of atelosteogenesis type 1.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Almost all cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Atelosteogenesis type 1 is a rare disorder; its exact prevalence is unknown. Only a few dozen affected individuals have been identified.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal fibula morphology · Frequent (79-30%)

An anomaly of the calf bone (fibula), one of the two bones of the calf.

Brachydactyly · Frequent (79-30%)

Digits that appear disproportionately short compared to the hand/foot. The word brachydactyly is used here to describe a series distinct patterns of shortened digits (brachydactyly types A-E). This is the sense used here.

Coronal cleft vertebrae · Frequent (79-30%)

Frontal schisis (cleft or cleavage) of vertebral bodies.

Limb undergrowth · Frequent (79-30%)

Limb shortening because of underdevelopment of one or more bones of the extremities.

Midface retrusion · Frequent (79-30%)

Posterior positions and/or vertical shortening of the infraorbital and perialar regions, or increased concavity of the face and/or reduced nasolabial angle.

Narrow chest · Frequent (79-30%)

Reduced width of the chest from side to side, associated with a reduced distance from the sternal notch to the tip of the shoulder.

Rhizomelia · Frequent (79-30%)

Disproportionate shortening of the proximal segment of limbs (i.e. the femur and humerus).

Short femur · Frequent (79-30%)

An abnormal shortening of the femur.

Other findings in the same source

From: Orphanet

Additional reported features include Talipes equinovarus (Frequent (79-30%)); Abnormal ossification involving the femoral head and neck (Frequent (79-30%)); Absent or minimally ossified vertebral bodies (Frequent (79-30%)); Pulmonary hypoplasia (Frequent (79-30%)); Thoracic hypoplasia (Frequent (79-30%)); Abnormal pancreatic duct morphology (Occasional (29-5%)); Cleft palate (Occasional (29-5%)); Enlarged cisterna magna (Occasional (29-5%)); Hypertelorism (Occasional (29-5%)); Joint dislocation (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Atelosteogenesis type 1 is Orthopaedics, with a orthopaedic specialist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• What explains the change in pain, movement or function?
• Which activities need adjustment while the diagnosis is being clarified?
• What are the roles of rehabilitation, observation and surgery in this situation?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Atelosteogenesis type 1. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.