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Boomerang dysplasia

Boomerang dysplasia



Overview

Boomerang dysplasia (BD) is a rare lethal skeletal dysplasia characterized by severe short-limbed dwarfism, dislocated joints, club feet, distinctive facies and diagnostic x-ray findings of underossified and dysplastic long tubular bones, with a boomerang-like bowing.

Symptoms 

• Severe Short-Limb Dwarfism: Extremely short arms and legs due to underdeveloped or absent limb bones.

• Boomerang-Shaped Femurs: Distinctive, pronounced bowing of the upper leg bones (femurs) that gives the condition its name.

• Joint Dislocations: Dislocations of the hips, knees, and elbows.

• Clubfeet: Inward- and upward-turning feet (talipes equinovarus).

• Skeletal & Spinal Underdevelopment: Underdeveloped or missing bones in the spine, rib cage, and pelvis, leading to a small, bell-shaped thorax (chest) and poor bone mineralization (underossification).

• Distinctive Facial Features (Facies): Midface hypoplasia (underdeveloped middle of the face), flat and broad nasal bridge, very small nostrils with a poorly formed septum (partition between the nostrils), micrognathia (small jaw), and sometimes a cleft palate.

• Brain and Abdominal Anomalies: In some cases, an encephalocele (a sac-like brain protrusion through the skull) or an omphalocele (an opening in the abdominal wall allowing organs to protrude near the navel).

• Hand and Foot Abnormalities: Short, broad hands and feet with shortened fingers (brachydactyly), hypoplastic (underdeveloped) nails, and occasional extra or missing digits (poly- or oligodactyly).

• Respiratory Failure: An underdeveloped rib cage and small lungs frequently cause severe breathing difficulties, meaning affected infants are typically stillborn or pass away shortly after birth from cardio-respiratory failure.

Causes

• FLNB Gene Mutations: Specific missense mutations or small in-frame deletions occur in the FLNB gene (often localized in regions encoding the actin-binding domain). Journal of Medical Genetics +1

• Abnormal Filamin B Protein: The mutation creates an altered filamin B protein that gains a new or atypical function. MedlinePlus (.gov) +1

• Impaired Cartilage Growth and Ossification: Filamin B normally helps regulate the growth, division, and maturation of cartilage-forming cells (chondrocytes) and the process where cartilage turns into bone (ossification). The mutant protein interferes with chondrocyte behavior and cell cleavage in the growth plate, leading to severe under ossification, absent bones, and bowed, rigid limbs

• Autosomal Dominant (New Mutations): The condition follows an autosomal dominant pattern of inheritance, meaning a change in only one copy of the FLNB gene in each cell is enough to cause the disorder.

• Sporadic Occurrence: Almost all cases happen as a new (de novo) spontaneous mutation during early fetal development, rather than being inherited from parents. Because the condition is typically lethal before or shortly after birth, affected individuals do not survive to pass the gene on

Diagnosis

• Skeletal Radiographs (X-rays): Postnatal or neonatal X-rays reveal hallmark features such as severe under-ossification (lack of bone mineralization), absent or underdeveloped long bones and vertebrae, joint dislocations (hips, knees, elbows), clubfeet, and the distinct boomerang-shaped bowing of the long tubular bones (especially the femurs).

• Genetic Testing: A definitive diagnosis is confirmed by identifying heterozygous or missense mutations / small in-frame deletions in the FLNB gene (which encodes filamin B).

• Prenatal Ultrasound and 3D-CT Scan: During pregnancy, detailed ultrasounds can sometimes spot severe limb shortening, thoracic (chest) hypoplasia, delayed bone mineralization, and joint dislocations, typically starting in the second trimester. A prenatal 3D-CT scan can help visualize the characteristic boomerang-shaped long bones.

• Chondro-Osseous Histopathology: Examination of cartilage and bone tissue samples can also support the diagnosis, though genetic and radiographic findings are more specific.

Treatment

• Supportive Care: Because the condition involves severe underdevelopment of the rib cage and lungs, affected infants typically experience fatal cardiorespiratory failure shortly after birth or are stillborn. Medical care at birth focuses on comfort measures, neonatal resuscitation, and ventilatory support if appropriate.

• Multidisciplinary Team: If a diagnosis is suspected or confirmed prenatally via ultrasound or genetic testing (which can identify mutations in the FLNB gene), care involves a team of perinatologists, geneticists, and neonatologists.

• Genetic Counseling: Families navigating a diagnosis or planning future pregnancies benefit from genetic counseling to discuss inheritance patterns and recurrence risks.

Type of Doctor Department : Pediatric Orthopedic Surgeon

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