Caudal regression syndrome, or sacral agenesis, is a rare birth defect. It is a congenital disorder in which the fetal development of the lower spine—the caudal partition of the spine—is abnormal. It occurs at a rate of approximately one per 25,000 live births. Some babies are born with very small differences compared to typical development, and others have significant changes. Most grow up to be otherwise normal adults who have difficulty with walking and incontinence.
Signs and symptoms
This condition exists in a variety of forms, ranging from partial absence of the tail bone regions of the spine to absence of the lower vertebrae, pelvis and parts of the thoracic and/or lumbar areas of the spine. In some cases where only a small part of the spine is absent, there may be no outward sign of the condition. In cases where more substantial areas of the spine are absent, there may be fused, webbed or smaller lower extremities and paralysis. Bowel and bladder control is usually affected.
Cause
The condition arises from some factor or set of factors present during approximately the 3rd week to 7th week of fetal development. Formation of the sacrum/lower back and corresponding nervous system is usually nearing completion by the 4th week of development. Due to abnormal gastrulation, the mesoderm migration is disturbed. This disturbance results in symptoms varying from minor lesions of the lower vertebrae to more severe symptoms such as complete fusion of the lower limbs. While the exact cause is unknown, it has been speculated that the condition has a combination of environmental and genetic causes, and that various types of the condition may have differing causes. Sacral agenesis syndrome is a well-established congenital anomaly associated with maternal diabetes mellitus. However, other causes are presumably involved, as demonstrated by the rare incidence of caudal regression syndrome compared to diabetes. The dominant inherited sacral agenesis is very often correlated with a mutation in the Hb9 gene. It was previously thought to be related to sirenomelia but has now been determined not to be related to this condition.
Prognosis
There are four levels of malformation. The least severe indicates partial deformation of the sacrum. The second level indicates a bilateral deformation. The most severe types involve a total absence of the sacrum. Depending on the type of sacral agenesis, bowel or urinary bladder deficiencies may be present. A permanent colostomy may be necessary in the case of imperforate anus. Incontinence may also require some type of continence control system be utilized. The condition often impacts the formation of the knees, legs or feet that is sometimes addressed through surgery. For some with tightly webbed, bent knees or knees that are fused straight, disarticulation surgery at the knee may be a viable option to maximize mobility options. Before more comprehensive medical treatment was available, full amputation of the legs at the hip was often performed. More recently, the 'amputation' is done at the knee for those who have bent knee positions and webbing between thigh and calf to enable more ease of mobility and better seating. Some children with knee disarticulation use prosthetic legs to walk. Prosthetics for children without substantial hip and trunk control is usually abandoned in favor of faster and easier wheelchair mobility as the child's weight and age increases. Children may 'walk' on their hands and generally are able to climb and move about to accomplish whatever they need and want to accomplish. Children more mildly affected may have normal gait and no need for assistive devices for walking. Others may walk with bracing or crutches. There is typically no cognitive impairment associated with this disability. Adults with this disability live independently, attend college, and have careers in various fields. In 2012, Spencer West, a man with sacral agenesis and both legs amputated, climbed Mt. Kilimanjaro using only his hands.
