The authors present two cases of SCID in children <4 months of age with respiratory distress at a tertiary care centre due to a recently described homozygous CD3 delta mutation found only in the Mexican Mennonite population.
The phenotype is usually T-B+NK+ SCID with lymphopenia where the clinical findings may be mild (CD3γ) or severe (CD3δ, ε, ζ) owing to the underlying molecular defect.
Homozygous mutations in CD3D and CD3E genes lead to a complete block in T-cell development and thus to an early-onset severe combined immunodeficiency phenotype.