Bone Abstracts

Infantile spinal muscular atrophy X-linked 2 (SMAX2) is a rare form of spinal muscular atrophy manifesting in severe hypotonia, areflexia, arthrogryposis, facial weakness and cryptorchidism, as frequently accompanied by bone fractures.

We present a boy patient with SMAX2 who presented typical symptoms from birth, as preceded by reduced fetal movements in the second and third trimester of pregnancy. In the first days of life the patient was found to have suffered fractures of the right femur and right humerus. Clinical examination revealed a myopathic face with characteristic tent-shape open mouth, tongue fibrillations, profound muscle weakness, areflexia, multiple contractures, cryptorchidism and mild skeletal abnormalities. Due to observed bone fractures, bone mineral density was estimated using dual x-ray absorptiometry (DXA) method in Infant program, which bore a result of BMD TBLH 0.273 g/cm². Molecular analysis revealed de novo c.1731C>T substitution in the UBA1 gene.

It is concluded that the diagnostic clinical criteria of SMAX2 should be expanded by a history of decreased fetal movement and the presence of skeletal abnormalities. Exon 15 of UBA1 is a specific hot spot for mutations.

Disclosure: The authors declared no competing interests.