Compound heterozygous mutations in SEC23B gene were detected by the use of a gene-targeted next-generation sequencing panel: the already reported missense mutation c.40C>T (p.Arg14Trp), and a new frameshift deletion (c.489_489delG, p.Val164Trpfs*3), confirming the diagnosis of CDA type II.
Sequence analysis of CDA-related genes revealed that the proband with CDA Ι in the first family was a compound heterozygote of CDAN1 with mutation IVS-12+2T>C and c. 3389C>T, while both probands with CDA ΙΙ in the second family were a homozygote of the SEC23B gene with mutation c.938G>A (R313H).
The unveiling of the genes mutated in the major CDA subgroups (I-CDAN1 and II-SEC23B) has now been completed with the recent identification of the CDA III gene (KIF23).
Three main types of CDA have been distinguished: CDA I and CDA III, whose loci have been already mapped, and CDA II (MIM 224100), the most frequent among CDAs, which is transmitted as an autosomal recessive trait and is known also as "HEMPAS" (hereditary erythroblast multinuclearity with positive acidified serum).