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Caudal regression syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Caudal regression syndrome

Caudal regression syndrome is a rare, complex developmental disorder that impairs the formation of the lower spine, spinal cord, limbs, and vital lower-body organ systems.

Overview & Symptoms

Caudal regression syndrome is a disorder that impacts the development of the lower (caudal) part of the spine. It can affect many parts of the lower body, including the lower back, limbs, genitourinary tract, and gastrointestinal tract.

The signs and symptoms of caudal regression syndrome vary widely among affected individuals:

  • Spinal Abnormalities: The bones of the lower spine (vertebrae) are misshapen or missing, and the end of the spinal cord may be malformed, missing, or abnormally connected (tethered) to nearby tissues. An abnormal curvature of the spine (scoliosis) is common. Rarely, spinal abnormalities affect the size and shape of the chest, leading to breathing problems.
  • Lower Limb and Mobility Issues: Small hip bones, flat and dimpled buttocks, and underdeveloped leg bones. Joints in the lower limbs may be stiff and difficult to move. Some individuals have legs bent in a "frog leg-like" position with webbed skin behind the knees, while others have straight, unbending knees. Feet may turn inward and upward (clubfoot) or outward and upward (calcaneovalgus). Sensation in the lower limbs may be reduced or excessive. Mobility ranges from walking independently to requiring braces, crutches, walkers, or wheelchairs.
  • Genitourinary Defects: Damage to the nerves controlling the bladder can cause neurogenic bladder, making it difficult to control urine flow. Kidneys may be malformed, including a missing kidney (unilateral renal agenesis), fused kidneys (horseshoe kidney), or duplicated ureters. These issues can cause frequent urinary tract infections, urine backflow (reflux), and progressive kidney failure. Genital abnormalities can include the urethra opening on the underside of the penis (hypospadias), undescended testes (cryptorchidism), abnormal connections between the rectum and vagina (rectovaginal fistula), or underdeveloped genitalia (genital agenesis).
  • Gastrointestinal Anomalies: Abnormal twisting (malrotation) of the large intestine, an obstruction of the anal opening (imperforate anus), soft out-pouchings in the lower abdomen (inguinal hernia), and frequent constipation or poor bowel control.
  • Upper Body Effects: Some individuals may also experience heart conditions or hearing problems.

Frequency

The frequency of caudal regression syndrome is unknown, but it is estimated to occur in 1 to 2.5 in 100,000 newborns. The condition is significantly more common among infants whose parent has diabetes while pregnant, affecting an estimated 1 in 350 newborns in this group.

Causes

Caudal regression syndrome is a complex condition likely caused by an interaction of multiple genetic and environmental factors:

  • Maternal Diabetes: Increased blood sugar (glucose) levels and related metabolic problems during pregnancy can have a harmful effect on the developing fetus, especially if the diabetes is poorly managed.
  • Mesoderm Disruption: Some researchers believe a disruption of fetal development around day 28 of pregnancy impairs the middle layer of embryonic tissue (the mesoderm), preventing normal formation of the skeleton, gastrointestinal system, and genitourinary system.
  • Vascular Disruption: Other researchers suggest an abnormal artery in the abdomen diverts blood flow away from the lower areas of the developing fetus, interfering with caudal development.

Many scientists believe the cause is a combination of both abnormal mesoderm development and decreased blood flow to the caudal areas of the fetus.

Inheritance

Caudal regression syndrome occurs sporadically, meaning it occurs in people with no history of the condition in their family. Multiple genetic and environmental factors likely affect the risk of developing this condition.

Other Names for This Condition

  • Caudal dysgenesis syndrome
  • Caudal dysplasia sequence
  • Caudal regression sequence
  • CRS
  • Lumbo-sacral agenesis
  • SA/CRS
  • Sacral agenesis
  • Sacral defect with anterior meningocele

Frequently Asked Questions

Look for a low‑set or absent sacral vertebrae on prenatal ultrasound, a flattened buttocks, clubfoot or other foot deformities, a small or absent anal opening, and early urinary problems such as poor bladder emptying. Physical exam may reveal a “frog‑leg” posture, skin dimpling over the lower back, or a palpable spinal defect.
Urodynamic studies measure bladder pressure, capacity, and sphincter function. Treatment usually starts with clean intermittent catheterization to empty the bladder completely, combined with anticholinergic medication (e.g., oxybutynin) to reduce over‑activity. In refractory cases, surgical options such as bladder augmentation or sphincter reconstruction may be considered.
Prognosis varies widely. Those with limited spinal involvement and good bladder control can lead independent lives with assistive devices. Severe forms with extensive vertebral agenesis, renal anomalies, or high spinal cord tethering often require lifelong medical support and have a higher risk of respiratory or renal complications, which can shorten life expectancy. Regular multidisciplinary follow‑up (neurology, urology, orthopedics, nephrology) improves quality of life.
Early serial casting or bracing can correct mild clubfoot or calcaneovalgus. For more severe joint contractures, soft‑tissue releases, osteotomies, or guided growth procedures are performed. Custom orthotics and gait‑training with physical therapy often enable ambulation with walkers or crutches; in some cases, a powered exoskeleton may be an option.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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