Citrullinemia type 1 is an autosomal recessive disease resulting in ammonia accumulation in the blood, and if uncontrolled may progress to coma or death in the early months after birth. 7 families from Southwest Iran having one or more children in their families or relatives, who died in the early months after birth due to citrullinemia type 1 visited for genetic counseling and prenatal diagnosis. Whole-exome sequencing was performed on peripheral blood specimens and chorionic villus samples. Sanger sequencing confirmed the genetic results. Both parents were identified as carriers for the exon 15 c.1168G A mutation in each family. The fetus in 6 out of 7 families was homozygote for A substitution on the argininosuccinate synthetase 1 gene. The presence of a common mutation in the argininosuccinate synthetase 1gene in all affected families of Southwest Iran shows a possible population cluster in this area.