X-linked distal arthrogryposis multiplex congenital (SMAX2) is a rare form of spinal muscular atrophy characterized by the neonatal onset of severe hypotonia, areflexia, profound weakness, multiple congenital contractures, facial dysmorphic features (myopathic face with open, tent-shaped mouth), cryptorchidism, and mild skeletal abnormalities (i.e. kyphosis, scoliosis), that is often preceded by polyhydramnios and reduced fetal movements <i>in utero</i> and followed by bone fractures shortly after birth. SMAX2 patients often have a limited life span, often succumbing to the disease within 2 years, as muscle weakness is progressive and chest muscle involvement eventually leads to ventilatory insufficiency and respiratory failure.
