Table 1 Clinical details of the four patients with homozygous SMN1 gene deletions and only one SMN2 gene copy
Patient, sexPregnancyMode of delivery (WG)Respiratory distressJoint contracturesAge at death (days)Heart defectAdditional findings
1, MPolyhydramnios, reduced fetal movementsSpontaneous (37)BirthHips, knees, ankles, elbows, wrists9Large sinus venosus ASD, multiple VSDs, PDASimian crease both hands, upslanting palpebral fissures, chromosomes normal*
2, FPolyhydramnios, reduced fetal movementsSpontaneous (41)BirthKnees, ankles, elbows, wrists11Common atrium, PDAChromosomes normal
3, FFetal arrhythmia from 37 WG, polyhydramniosPrimary section (40)BirthKnees, ankles18Not reportedBladder paralysis, tachycardia, bradycardia
4, FNormalSecondary section (41)BirthNot present122Large ASDII, subaortal VSD, dilated right ventricleNo eyelid closure, chromosomes normal
  • ASD, atrial septal defect; F, female; M, male; PDA, patent ductus arteriosus; VSD, ventricular septal defect; WG, weeks gestation.

  • *Routine chromosome analyses gave normal results in 62 metaphases. Interphase cytogenetic analysis by fluorescence in situ hybridisation showed two signals for chromosome 21 in 91/100, three signals in 6/100, four signals in 1/100 and one signal in 2/100 analysed lymphocyte nuclei. This result was not considered statistically significant to assume a trisomy 21 mosaicism.