Recessive mutations in four distinct genes have been identified in congenital/infantile SMA with arthrogryposis or fractures, including survival motor neuron 1 (SMN1) [33], thyroid hormone receptor interactor 4 (TRIP4), activating signal cointegrator 1 complex subunit 1 (ASCC1) [34], and ubiquitin-like modifier-activating enzyme 1 (UBA1). Here, SMN1 is linked to proximal spinal muscular atrophy.