Asphyxiating Thoracic Dysplasia (ATD) ((MIM 208500, MIM 6112633, MIM 613091, MIM 61819, MIM614376) belongs to the short rib polydactyly group and is characterized by a long and narrow thorax, short long bones and trident acetabular roof. Polydactyly, retinal degeneration, cystic renal and liver diseases have been occasionally reported. Today, mutations in IFT80 (MIM 611177), DYNC2H1 (MIM 603297), TCC21B (MIM 612014) and WDR19 (MIM 608151) genes have been reported in ATD. Through a national grant (PHRC, AOM 06031), we have collected 55 ATD cases including 29 fetuses issued from 42 families who benefit the combined approach of deep phenotyping and molecular screening of IFT80 and DYNC2H1. The series included 26 alive cases ranging in age from 6 months to 36 years. Respiratory treatment was needed in 46%, including positive pression respiration, and invasive or non-invasive ventilation. Cystic renal and liver diseases occur in 16% of cases; whereas retinal degeneration was present in 40 % cases aged more than 2 years (6/15). The molecular screening allowed us to detect DYNC2H1 mutations in 63% and IFT80 mutations in 6%. In 6 cases, only one heterozygote mutation in either IFT80 or DYNC2H1 was identified. Finally, the two genes were excluded in 31% cases. These preliminary results emphasize that DYNC2H1 is the major gene responsible for ATD. The presence of only one mutation (27% of mutated cases) may suggest a digenic diallelic inheritance. Ongoing studies will hopefully lead to the identification of other disease genes.