Salih Myopathy

Clinical characteristics: Salih myopathy is characterized by muscle weakness (manifest during the neonatal period or in early infancy) and delayed motor development; children acquire independent walking between ages 20 months and four years. In the first decade of life, global motor performance is stable or tends to improve. Moderate joint and neck contractures and spinal rigidity may manifest in the first decade but become more obvious in the second decade. Scoliosis develops after age 11 years. Cardiac dysfunction manifests between ages five and 16 years, progresses rapidly, and leads to death between ages eight and 20 years, usually from heart rhythm disturbances.

Diagnosis/testing: The diagnosis is established in a proband by identification of biallelic pathogenic variants in the first three M-line-encoding exons (Mex1, Mex2, and Mex3) of TTN, the only gene in which pathogenic variants are known to cause Salih myopathy.

Management: Treatment of manifestations: Care, best provided by a multidisciplinary team, includes stretching exercises and physical therapy; assistive mechanical devices for sitting and ambulation as needed; and appropriate technical support in educational settings. Treat heart failure and cardiac arrhythmia as soon as they are evident. Cardiac transplantation may be considered for progressive dilated cardiomyopathy and heart failure refractory to medical therapy.

Prevention of secondary complications: Annual influenza vaccine and other respiratory infection-related immunizations are advised. Aggressive treatment of lower-respiratory tract infections.

Surveillance: Electrocardiogram (EKG), 24-hour Holter EKG, and echocardiogram every six months beginning at age five years. Annual evaluation of respiratory function beginning at age 10 years. Clinical examination and x-ray as needed for orthopedic complications (e.g., foot deformity, joint contractures, spinal deformity).

Agents/circumstances to avoid: Ibuprofen in those with congestive heart failure.

Genetic counseling: Salih myopathy is inherited in an autosomal recessive manner. The parents of an affected child are obligate heterozygotes (i.e., carriers of one pathogenic variant) and are asymptomatic. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal testing for a pregnancy at increased risk are possible if the pathogenic variants in the family have been identified.