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Condition report · Musculoskeletal

Bailey-Bloch Congenital Myopathy

Whole genome sequencing reads the STAC3 gene for changes in both copies that cause Bailey-Bloch congenital myopathy, a muscle condition present from birth that raises the risk of a reaction to some anaesthetics.

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About this condition

A rare muscle condition present from birth, causing weakness, a cleft palate and a raised risk of a severe reaction to some anaesthetics. It is caused by changes in both copies of the STAC3 gene and was first described in the Lumbee Native American community.

Bailey-Bloch congenital myopathy, also called STAC3 disorder, is a rare muscle condition that is present from birth. Babies typically have weakness, low muscle tone, feeding difficulties and delayed motor milestones. A cleft palate, droopy eyelids, a small jaw and short stature are common, and joint contractures and curvature of the spine often develop. Intellect is usually normal.

The condition is caused by changes in both copies of STAC3. This gene is needed for the signal that triggers muscle contraction, through the machinery that releases calcium inside muscle cells. It was first described in the Lumbee people of North Carolina and has since been reported in many other populations. People with the condition are also susceptible to malignant hyperthermia, a dangerous reaction to certain anaesthetic drugs.

The condition is inherited in an autosomal recessive way. Parents are usually carriers, so carrier testing for relatives and genetic counselling are available. The main safety step is to inform anaesthetists, so that drugs that can trigger malignant hyperthermia are avoided. Physiotherapy, orthopaedic and cleft palate care, and monitoring of breathing and swallowing are also important.

The condition we analyse

Autosomal recessive

Caused by changes in both copies of STAC3, which is needed for the signal that triggers muscle contraction. The condition was first described in the Lumbee people of North Carolina and has since been reported in many other populations.

Signs and symptoms

Weakness and low muscle tone from birth, with cleft palate, droopy eyelids, a small jaw and short stature. Joint contractures and curvature of the spine (kyphoscoliosis) often develop. People are susceptible to malignant hyperthermia, a dangerous reaction to certain anaesthetic drugs.

What a diagnosis changes

Anaesthetists should be informed so that drugs that trigger malignant hyperthermia, such as volatile anaesthetic gases and suxamethonium, are avoided. Physiotherapy, orthopaedic and cleft palate care and monitoring of breathing and swallowing are important. Parents are usually carriers, so carrier testing for relatives and genetic counselling are available.

Genes analysed

Also known as

congenital myopathy - cleft palate - malignant hyperthermia; congenital myopathy cleft palate and malignant hyperthermia; congenital myopathy-cleft palate-malignant hyperthermia syndrome; myopathy, congenital, baily-bloch; NAM; Native American myopathy; STAC3 disorder

MONDO:0009722OMIM 255995Orphanet 168572MedGen 340586Sources: [1][2][3]

Why whole genome sequencing

Knowing the STAC3 result matters for anaesthesia as well as for family planning.

Planning for anaesthesia

Anaesthetists should be told about the condition, so that volatile anaesthetic gases and suxamethonium are avoided. If malignant hyperthermia does occur, it is treated with dantrolene, which needs to be given early. Early recognition is essential.

Carrier testing for relatives

Parents of an affected child are usually carriers, and carrier testing for relatives is available. Genetic counselling explains the recessive pattern and the options for family planning.

References

  1. Webb BD, Manoli I, Jabs EW, 2019. STAC3 Disorder. GeneReviews
  2. Zaharieva IT, Sarkozy A, Munot P, Manzur A, O'Grady G, Rendu J et al., 2019. STAC3 variants cause a congenital myopathy with distinctive dysmorphic features and malignant hyperthermia susceptibility. Human mutation
  3. STAC3 disorder. MedlinePlus Genetics

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