Caudal regression sequence (CRS) affects the development of the lower (caudal) half of the body. It can impact the development of the lower back, spinal cord, and lower limbs. The kidneys, bladder, digestive tract, and genitalia may also be affected. CRS occurs during fetal development and is present at birth. The features and severity vary from person to person. In some cases, CRS is severe and can be life-threatening. In other cases, people with CRS may have problems with bowel and bladder control and be unable to walk. CRS is not known to affect the development of the brain and intelligence is generally average. The cause of CRS is unknown, and is thought to be due to a combination of genetic and environmental factors. Maternal diabetes, exposure to retinoic acid, and disorders of blood flow are thought to increase the chance for a woman to have a baby with CRS, but most babies with CRS are born to women without any known risk factor. CRS is diagnosed based on the features. Other conditions may need to be excluded before a diagnosis of CRS can be made. Treatment is focused on managing the symptoms and usually includes surgery, physical therapy, and devices to help with sitting and walking.

Symptoms may include:

• Abnormalities of the lower spine and spinal cord
• Underdevelopment of the legs
• Underdeveloped hips
• Fused kidneys or underdeveloped kidneys
• Damage to the nerves to the bladder
• Urethral opening on the underside of the penis (hypospadias)
• Abnormal connection between the rectum and the vagina
• Twisted intestine (malrotation of the large intestine)
• Underdevelopment of the heart

People with CRS may develop curvature of the spine (scoliosis) which may sometimes affect breathing. The leg bones are often underdeveloped, and many people with CRS have difficulty with sitting and walking. Kidney abnormalities may lead to frequent urinary tract infections or kidney failure that gets worse over time. Difficulty with bladder and bowel control may occur. In some cases, the symptoms of CRS are severe and life-threatening.

Certain conditions in pregnancy may increase the chance to have a baby with CRS. These include maternal diabetes, exposure to retinoic acid, and abnormalities in blood flow. Several genes have been identified that may also influence the chance to have a baby with CRS. In most people with CRS, the cause has not been identified.

Very severely affected newborns may not survive due to cardiac (heart), renal, and/or respiratory complications. In others, the vital systems may be unaffected or minimally affected. Those that survive typically have normal intelligence, with neuromuscular deficits of the lower limbs and sphincters (muscles that control the passage of urine and bowel movements). Secondary neurogenic bladder, leading to progressive renal damage and deterioration of renal function, remains a concern. Therefore, extensive and long-term follow-up of urologic issues is needed.