Caudal regression syndrome, also called Sacral Agenesis, is a disorder that impairs the development of the lower (caudal) half of the body. Affected areas can include the lower back and limbs, the genitourinary tract, and the gastrointestinal tract.

In this disorder, the bones of the lower spine (vertebrae) are frequently misshapen or missing, and the corresponding sections of the spinal cord are also irregular or missing. Affected individuals may have incomplete closure of the vertebrae around the spinal cord, a fluid-filled sac on the back covered by skin that may or may not contain part of the spinal cord, or tufts of hair at the base of the spine. People with caudal regression syndrome can also have an abnormal side-to-side curvature of the spine (scoliosis). The spinal abnormalities may affect the size and shape of the chest, leading to breathing problems in some individuals.

Individuals with caudal regression syndrome may have small hip bones with a limited range of motion. The buttocks tend to be flat and dimpled. The bones of the legs are typically underdeveloped, most frequently the upper leg bones (femurs). In some individuals, the legs are bent with the knees pointing out to the side and the feet tucked underneath the hips (sometimes called a frog leg-like position). Affected individuals may be born with inward- and upward-turning feet (clubfeet), or the feet may be outward- and upward-turning (calcaneovalgus). Some people experience decreased sensation in their lower limbs.

Abnormalities in the genitourinary tract in caudal regression syndrome are extremely varied. Often the kidneys are malformed; defects include a missing kidney (unilateral renal agenesis), kidneys that are fused together (horseshoe kidney), or duplication of the tubes that carry urine from each kidney to the bladder (ureteral duplication). These kidney abnormalities can lead to frequent urinary tract infections and progressive kidney failure. Additionally, affected individuals may have protrusion of the bladder through an opening in the abdominal wall (bladder exstrophy). Damage to the nerves that control bladder function, a condition called neurogenic bladder, causes affected individuals to have progressive difficulty controlling the flow of urine. Genital abnormalities in males can include the urethra opening on the underside of the penis (hypospadia) or undescended testes (cryptorchidism). Females may have an abnormal connection between the rectum and vagina (rectovaginal fistula). In severe cases, both males and females have a lack of development of the genitalia (genital agenesis).

People with caudal regression syndrome may have abnormal twisting (malrotation) of the large intestine, an obstruction of the anal opening (imperforate anus), soft outpouchings in the lower abdomen (inguinal hernias), or other malformations of the gastrointestinal tract. Affected individuals are often constipated and may experience loss of control of bladder and bowel function.

 

Taken from the Genetics Home Reference at http://ghr.nlm.nih.gov/condition/caudal-regression-syndrome