Myotubular myopathy (XLMTM) is an X-linked disorder caused by mutations in the myotubularin gene (MTM1). The clinical spectrum is variable and ranges from individuals who require a wheelchair and full time breathing support to those who are able to walk and breathe on their own. Symptoms of myotubular myopathy include long faces, facial weakness with eye muscle weakness, breathing support with a muscle biopsy demonstrating central nucleated fibers. These symptoms may be caused by mutations or changes in the MTM1, BIN1 (bridging integrator 1), DNM2 (dynamin 2) and RYR1 (ryanodine receptor 1) genes. However, the majority are caused by mutations in the MTM1 gene. Some patients with symptoms consistent with myotubular myopathy who initially have negative testing of the MTM1 gene were later found to have a unique type of change in the MTM1 gene. This unique change, called a deletion or duplication, can be found with a different type of genetic test called a CGH (comparative genomic hybridization) array.

Investigators do not know how frequent deletions and duplications are in patients with X-linked myotubular myopathy. Recently, there have been advances in identifying potential treatments for XLMTM. The next step will be to proceed with clinical trials of potential treatments. In order to be ready for clinical trials, it is important that investigators find the specific genetic change that is causing XLMTM in people with this diagnosis. This study will attempt to find changes in the MTM1 gene in individuals who have clinical symptoms consistent with a diagnosis of XLMTM. Participants will be asked to enroll in the CMDIR (Congenital Muscle Disease International Registry), complete a brief clinical survey, provide access to medical records, and provide a saliva or blood sample for genetic testing. Results of genetic testing will be communicated to participants by the physician specified in the consent by the signing person.

Study Hypothesis:

Not all individuals with a clinical diagnosis of XLMTM have access to genetic testing. Investigators know that deletions and duplications of the MTM1 gene can cause XLMTM. Investigators will find more individuals with XLMTM by performing genetic testing of the MTM1 gene, including CGH array for deletions and duplications.

• Prospective participants will complete registration in the CMDIR.
• The CMDIR genetic curator will review CMDIR data for study eligibility.
• If eligible, participant will be called and consented to participate in the study.
• Sequencing can be done with a saliva sample. However, if this method does not detect a mutation or change in the MTM1 gene, a further test, called CGH Array, has to be performed. For the CGH Array test, a saliva sample may deliver a clear result in terms of a deletion/duplication mutation. In the event, CGH Array with the saliva sample does not provide a result, a the blood sample is necessary to repeat CGH Array.
• The study participant will receive a kit and instructions for saliva specimen collection for genetic testing from the CMDIR in the mail.
• If a mutation or change in the MTM1 gene could not be found by genetic testing and CGH Array with a saliva sample, the study participant will receive a second kit in the mail from the CMDIR with instructions for a blood draw to be used for CGH Array.
• The family will coordinate collection of the saliva specimen or a local blood draw, if necessary, and will be responsible for mailing the specimen in a pre-paid parcel to the University of Chicago. There will be a $40 reimbursement for the cost of the blood draw. Mailing the specimen to the testing site is at no cost for the participant. A two-week turn-around from receipt of the kit to sending it to the testing laboratory is requested.
• Genetic testing will start with standard sequencing of the MTM1 gene, isolated from the saliva specimen, followed by CGH Array if sequencing of the MTM1 gene isolated from the saliva sample or further from a blood sample if a variant consistent with the symptoms could not be detected using the saliva sample.
• Test results will be 1) reported to a physician specified by the study participant and 2) uploaded into the study participant's profile in the CMDIR and 3) if concurrently enrolled in the Beggs Laboratory or other IRB-approved clinical study, test results will also be made available to that study provided appropriate informed consent has been given.

Inclusion Criteria: Patient eligibility will be determined by the CMDIR genetic curator using the following prioritization protocol.

1. Males and females in the US and Canada who have a known mutation in the MTM1 gene identified in a research lab and never confirmed in a clinical CLIA (Clinical Laboratory Improvement Amendments) -certified laboratory.
2. Male and female patients in the US and Canada who meet 2 of 3 of the following criteria: + clinical history, + family history, + centronucleation on muscle biopsy (no signs of nemaline rods or cores). Clinical history includes: post-natal breathing support (not necessarily continued after first month), length above 90% for EGA (estimated gestational age), facial characteristics (narrow facies), facial weakness (ophthalmoplegia, excessive saliva with need for suctioning).
3. Males and females in the US and Canada who present with XLMTM symptoms and no genetic mutation in the MTM1 gene found with conventional sequencing, requiring CGH array deletion/duplication testing.
4. Age range: One month - no maximum age.
5. Individual is registered with the CMDIR.
6. Written study consent provided by parent/caregiver (affected individual's age less than 18 years or for those individuals greater than 18 years with learning disabilities or inability to physically access consent) or affected individual (age greater than 18 years)

Exclusion Criteria:

1. Carrier testing for asymptomatic mothers.

The study will be composed of individuals registered in the CMDIR who have been clinically diagnosed with XLMTM but do not have an XLMTM diagnosis confirmed by genetic testing.