Courtesy: Amr Abdelgawad, Maimonaiedes Medical Centre, New York, USA

Overview

Genetic abnormalities frequently affect the musculoskeletal system.
Many skeletal dysplasias, connective tissue disorders, and neuromuscular diseases have identifiable gene mutations.
Understanding these genes helps explain clinical features and inheritance patterns.

Genetic Disorders with Musculoskeletal Manifestations

Osteogenesis imperfecta – mutation in COL1A1 gene affecting type I collagen.
Achondroplasia – mutation in fibroblast growth factor receptor 3 (FGFR3).
Marfan syndrome – mutation in FBN1 gene affecting fibrillin.
Diastrophic dysplasia – mutation in SLC26A2 gene affecting sulfate transport in cartilage.
Pseudoachondroplasia – mutation in cartilage oligomeric matrix protein (COMP).
Multiple epiphyseal dysplasia – commonly associated with COMP gene mutation.
Spondyloepiphyseal dysplasia – mutation in type II collagen gene (COL2A1).
Duchenne muscular dystrophy – mutation in dystrophin gene causing progressive muscle degeneration.
Becker muscular dystrophy – mutation in dystrophin gene with milder clinical severity.
Fibrous dysplasia – mutation in GNAS gene affecting G protein signaling.
Osteopetrosis – defects in osteoclast function including mutations in CLCN7 or TCIRG1.
Multiple hereditary exostoses – mutations in EXT1 or EXT2 genes.
Neurofibromatosis type 1 – mutation in NF1 gene located on chromosome 17.
Charcot–Marie–Tooth disease – frequently associated with mutation in PMP22 gene.
Spinal muscular atrophy – mutation in survival motor neuron (SMN) gene.

Turner syndrome – short stature associated with SHOX gene deficiency.
Vitamin D dependent rickets type 1 – mutation affecting vitamin D activation enzymes.
Cleidocranial dysplasia – mutation in RUNX2 gene affecting bone formation.
Apert syndrome – mutation in fibroblast growth factor receptor 2 (FGFR2).
X-linked hypophosphatemic rickets – mutation in PHEX gene affecting phosphate metabolism.
Friedreich ataxia – mutation in FXN gene.
Clubfoot – associated with PITX1 and TBX4 genes involved in limb development.
Fibular hemimelia – associated with abnormalities in sonic hedgehog signaling.
Fibrodysplasia ossificans progressiva – mutation in ACVR1 gene causing heterotopic ossification.

Autosomal dominant – disease occurs when one mutated gene is inherited.
Examples include achondroplasia, Marfan syndrome, multiple hereditary exostoses, cleidocranial dysplasia, and neurofibromatosis type 1.
Autosomal recessive – disease occurs only when two mutated genes are inherited.
Examples include diastrophic dysplasia, hypophosphatasia, homocystinuria, vitamin D dependent rickets, and sickle cell disease.
X-linked recessive – mutation occurs on the X chromosome and mainly affects males.
Examples include Duchenne muscular dystrophy, Becker muscular dystrophy, hemophilia, and Hunter syndrome.
X-linked dominant – less common inheritance pattern.
Examples include X-linked hypophosphatemic rickets and Leri–Weill dyschondrosteosis.

RUNX2 (core binding factor alpha 1) is a transcription factor essential for osteoblast differentiation.
Mutation of RUNX2 causes cleidocranial dysplasia with absent or hypoplastic clavicles.

Wnt proteins bind to LRP5 and LRP6 receptors on osteoblast precursor cells.
This interaction increases beta-catenin signaling.
Activation of beta-catenin promotes osteoblast differentiation and bone formation.
Inhibitory proteins such as sclerostin and DKK1 suppress this pathway.

Blocking sclerostin enhances Wnt signaling and stimulates bone formation.
Romosozumab is a monoclonal antibody against sclerostin used in osteoporosis treatment.

A rare autosomal dominant disorder characterized by progressive heterotopic ossification.
Caused by activating mutation in ACVR1 gene.
The mutation alters bone morphogenetic protein signaling and results in abnormal bone formation in soft tissues.

SOX9 is a major transcription factor regulating chondroblast differentiation.
It plays a central role in cartilage development and maintenance of chondrocyte lineage.

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