In advanced cases, neck extensor weakness can cause the head to lean towards the chest, termed head drop. Non-muscular
The most common non-musculoskeletal manifestation of FSHD is abnormalities in the small arteries (arterioles) in the retina. Tortuosity of the arterioles is seen in approximately 50% of those with FSHD. Less common arteriole abnormalities include telangiectasias and microaneurysms. These abnormalities of arterioles usually do not affect vision or health, although a severe form of it mimics Coats disease, a condition found in about 1% of FSHD cases and more frequently associated with large 4q35 deletions. High-frequency hearing loss can occur in those with large 4q35 deletions, but otherwise is no more common compared to the general population. Large 4q35 deletion can lead to various other rare manifestations.Scoliosis can occur, thought to result from weakness of abdominal, hip extensor, and spinal muscles. Conversely, scoliosis can be viewed as a compensatory mechanism to weakness. Breathing can be affected, associated with kyphoscoliosis and wheelchair use; it is seen in one-third of wheelchair-using patients. However, ventilator support (nocturnal or diurnal) is needed in only 1% of cases. Although there are reports of increased risk of cardiac arrhythmias, general consensus is that the heart is not affected. Genetics
The genetics of FSHD is complex. FSHD and the myotonic dystrophies have unique genetic mechanisms that differ substantially from the rest of genetic myopathies. The DUX4 gene is the focal point of FSHD genetics. Normally, DUX4 is expressed during embryogenesis and later repressed in all tissues except the testes.
Tetrasomy 18p is a genetic condition that is caused by the presence of an isochromosome composed of two copies of the short arm of chromosome 18 in addition to the two normal copies of the chromosome. It is characterized by multiple medical and developmental concerns. Signs and symptoms
Tetrasomy 18p causes a wide range of medical and developmental problems. Congenital anomalies
Cardiac anomalies are the most common congenital malformation in individuals with tetrasomy 18p. However, there is no pathognomatic heart defect associated with the condition. Patent ductus arteriosus is the most common defect. Septal defects (ventricular septal defects and atrial septal defects) are also common, as are patent foramina ovalia. Other cardiac anomalies include mitral valve regurgitation,  mitral valve prolapse, bicuspid pulmonary valve, hypoplastic transverse aortic arch, tricuspid valve regurgitation, right ventricular hypertrophy, and pulmonic stenosis. In males, cryptorchidism is common. Abnormal genitalia in females is not a common feature. Renal abnormalities have been reported in a minority of patients. Horseshoe kidney and bladder diverticuli have been reported. Other abdominal malformations, including pyloric stenosis and hernias, have also been reported, though they are present in only a minority of patients.Orthopedic anomalies also occur relatively frequently, with hip dysplasia being the most common orthopedic issue. Clubfoot and rocker bottom feet have also been reported.Myelomeningocele is another known feature associated with tetrasomy 18p. Neonatal complications
Neonatal complications (apart from congenital anomalies) are common.