What is Sacral agenesis / Caudal regression syndrome

Sacral agenesis, also known as caudal regression syndrome, is a rare congenital condition characterized by the abnormal development of the lower spine (sacrum) and, in some cases, the lumbar vertebrae. This developmental difference can impact the function of the lower limbs, bladder, bowels, and other internal organs, with severity ranging from mild spinal malformations to more complex systemic involvement.

What causes sacral agenesis and caudal regression syndrome?

The exact cause of sacral agenesis remains multifactorial. In the majority of cases, it is believed to result from a combination of genetic predisposition and environmental factors that disrupt the development of the caudal (tail) end of the embryo during the first few weeks of pregnancy. While the condition is strongly associated with maternal diabetes—occurring roughly 200 to 400 times more frequently in infants born to mothers with diabetes than in the general population—many cases occur sporadically without a clear, identifiable cause.

How does this condition affect the body?

Because the lower spine is essential for supporting the nervous system and internal organs, caudal regression syndrome can affect several bodily systems. The clinical presentation varies greatly among individuals, but common areas of impact include:

• Skeletal System: Underdevelopment or complete absence of the sacrum and coccyx, often leading to spinal curvature (scoliosis) or hip joint abnormalities.


• Neurological System: Potential damage to the nerves exiting the lower spine, which can result in muscle weakness, atrophy, or sensory loss in the lower extremities.


• Urological and Gastrointestinal Systems: Neurogenic bladder, bowel incontinence, or renal (kidney) anomalies are frequently observed.


• Lower Extremities: Variations in leg length, clubfoot, or joint contractures due to altered nerve signaling.

How is the condition classified?

Clinicians often use the Rens classification system to categorize sacral agenesis based on the extent of the spinal defect. This system helps medical teams predict potential orthopedic and neurological challenges. Generally, classifications range from Type I, where the defect is limited to a partial unilateral sacral agenesis, to Type IV, which involves a more complete absence of the sacrum and, occasionally, the involvement of the lumbar vertebrae.

What is the prevalence and who is affected?

Sacral agenesis is a very rare condition, with an estimated incidence ranging from 1 in 25,000 to 1 in 100,000 live births. It is a congenital condition, meaning it is present at birth. While it affects both males and females, some clinical literature suggests a slight male predominance. Because caudal regression syndrome is a complex, life-long condition, it requires a multidisciplinary medical approach involving pediatric orthopedists, urologists, and neurologists to manage the varying needs of the patient.

How is it differentiated from other conditions?

It is important to distinguish caudal regression syndrome from other spinal dysraphisms like spina bifida. While both involve spinal development, sacral agenesis is specifically defined by the developmental failure of the sacral vertebrae. At DiseaseMaps.org, we have 12 community members who have shared their experiences with this diagnosis, highlighting the importance of connecting with others who understand the unique journey of navigating a rare spinal condition.

Next steps

• Consult with a specialized pediatric orthopedic surgeon or a neurosurgeon to evaluate spinal stability.


• Work with a urologist to develop a comprehensive plan for bladder and bowel management.


• Connect with the DiseaseMaps.org community to share experiences and find support from others living with sacral agenesis.


• Seek guidance from a clinical geneticist to discuss potential underlying factors and recurrence risks for future family planning.

Medical disclaimer: This information is for educational purposes only and should not replace professional medical advice, diagnosis, or treatment from your healthcare provider.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Caudal Regression Syndrome.


• Orphanet: Sacral Agenesis.


• OMIM (Online Mendelian Inheritance in Man): Caudal Regression Sequence.


• National Institute of Neurological Disorders and Stroke (NINDS) publications on congenital spinal anomalies.