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Paediatric Laboratory Medicine

Trismus-Pseudocamptodactyly Syndrome: MYH8 Sequencing

Clinical Significance

Patients with trismus-pseudocamptodactyly syndrome may show cardiac myxomas, spotty skin pigmentation alone or in combination with cutaneous lesions. Most affected individuals have distal arthrogryposis, including pseudocamptodactyly of the hands and feet, trismus, or both, which improves symptomatically with aging.

Trismus-pseudocamptodactyly syndrome is an autosomal dominant disorder caused by a deficiency of a perinatal skeletal myosin heavy chain. The syndrome is caused by mutations in the MYH8 gene which has been mapped to chromosome 17p13.1. A single mutation, p.Arg674Gln, has been described in several families of Belgian descent.

Trismus-pseudocamptodactyly syndrome is present when an individual has one copy of the defective gene. There is a 50% chance that baby will inherit the mutation for trismus-pseudocamptodactyly syndrome and thus may develop symptoms in the perinatal period. There is a 50% chance that the baby will not have trismus-pseudocamptodactyly syndrome.

Test Name

Trismus-Pseudocamptodactyly Syndrome: MYH8 Sequencing

Alternate Name/ Synonym

  • Distal Arthrogryposis type 7
  • Hecht syndrome

Gene Name

  • MYH8

Test Code



Molecular Genetics



External Proficiency Testing


Turn Around Time

2 weeks (Prenatal samples), 2-3 weeks (Pregnancy/Urgent samples), 4-6 weeks (Routine)


Myosin heavy chain 8


Trismus-Pseudocamptodactyly Syndrome

Specimen Type

Blood; gDNA.

For details about specimen requirements, please refer to: Specimen Type & Requirements (PDF).

Minimum Specimen Requirements

5-10 mL EDTA or ACD 0.5 mL EDTA (neonate); minimum 10 ug in 100 uL low TE (pH8.0)


Room Temperature

Special Requirements

Special Instructions for Genome Diagnostics Samples

If sample shipment >48 hours, ship on ice.

Approval is not required

CPT Codes


Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Phone: 416-813-7200
Phone: 1-855-381-3212


Interpretation is provided in report