From OMIM
The term achondrogenesis has been used to characterize the most severe forms of chondrodysplasia in humans, invariably lethal before or shortly after birth. Achondrogenesis type I is a severe chondrodystrophy characterized radiographically by deficient ossification in the lumbar vertebrae and absent ossification in the sacral, pubic and ischial bones and clinically by stillbirth or early death (Maroteaux and Lamy, 1968; Langer et al., 1969). In addition to severe micromelia, there is a disproportionately large cranium due to marked edema of soft tissues. Classification of Achondrogenesis Achondrogenesis was traditionally divided into 2 types: type I (Parenti-Fraccaro) and type II (Langer-Saldino). Borochowitz et al. (1988) suggested that achondrogenesis type I of Parenti-Fraccaro should be classified into 2 distinct disorders: type IA (ACG1A; 200600), corresponding to the cases originally published by Houston et al. (1972) and Harris et al. (1972), and type IB, corresponding to the case originally published by Fraccaro (1952). Analysis of the case reported by Parenti (1936) by Borochowitz et al. (1988) suggested the diagnosis of achondrogenesis type II, i.e., the Langer-Saldino type (200610). Type IA would be classified as lethal achondrogenesis, Houston-Harris type; type IB, lethal achondrogenesis, Fraccaro type; and type II, lethal achondrogenesis-hypochondrogenesis, Langer-Saldino type. Superti-Furga (1996) suggested that hypochondrogenesis should be considered separately from achondrogenesis type II because the phenotype can be much milder.  http://www.omim.org/entry/600972

From MedlinePlus Genetics
Achondrogenesis is a group of severe disorders that affect cartilage and bone development. These conditions are characterized by skeletal abnormalities that cause serious health problems. As a result, most infants with achondrogenesis die before birth or soon after, often due to respiratory failure. 

Researchers have described three main types of achondrogenesis: type 1A, type 1B, and type 2. While these types differ in their genetic causes and inheritance patterns, they often have overlapping signs and symptoms. Genetic testing and medical imaging are often needed to tell them apart. 

All forms of achondrogenesis feature short arms and legs, a narrow chest, and underdeveloped lungs. Infants with achondrogenesis type 1A, which is also called TRIP11-related achondrogenesis, typically have ribs that fracture easily. Bone formation (ossification) is also severely reduced in the skull and spine.

Infants with achondrogenesis type 1B, which is also called SLC26A2-related achondrogenesis, often have short fingers and toes and feet that may turn inward and upward (clubfeet). Infants with achondrogenesis type 1B may also have a sac (pouch) formed from the inner lining of the abdominal cavity that pushes through a hole in the abdominal wall around the belly-button (umbilical hernia) or near the groin (inguinal hernia).

The ossification of the spine and pelvis may be severely reduced in infants with achondrogenesis type 2, which is also called COL2A1-related achondrogenesis. The distinctive facial features seen in infants with achondrogenesis type 2 include a prominent forehead, a small chin, and, in some cases, an opening in the roof of the mouth (cleft palate).

Achondrogenesis type 2 and a similar skeletal disorder called hypochondrogenesis were once thought to be distinct conditions. However, because these conditions have overlapping features and a shared genetic cause, they are now considered to be part of the same disease spectrum.   https://medlineplus.gov/genetics/condition/achondrogenesis