E83.32 Hereditary vitamin D-dependent rickets (type 1) (type 2)

Name of the Condition

• Hereditary vitamin D-dependent rickets (type 1) (type 2)

Summary

Hereditary vitamin D-dependent rickets (type 1) (type 2) refers to a group of genetic disorders characterized by impaired vitamin D metabolism or action, leading to rickets or osteomalacia. These conditions disrupt calcium and phosphate homeostasis, affecting bone mineralization and skeletal development. Type 1 involves defects in the enzyme 25-hydroxyvitamin D 1-alpha-hydroxylase, while type 2 results from mutations in the vitamin D receptor, both impairing the body's ability to utilize vitamin D effectively.

Causes

Causes are genetic, with type 1 linked to mutations in the CYP27B1 gene (encoding the 1-alpha-hydroxylase enzyme) and type 2 associated with mutations in the VDR gene (affecting the vitamin D receptor). These mutations disrupt the conversion of vitamin D to its active form or its binding to target tissues, leading to insufficient calcium absorption and bone mineralization.

Risk Factors

Risk factors include a family history of the disorder, as both types are inherited. Consanguinity may increase the likelihood of autosomal recessive forms, and gender can influence presentation (e.g., X-linked patterns in type 1). Symptoms often manifest in infancy or childhood during periods of rapid growth.

Symptoms

Symptoms include bone pain, muscle weakness, growth retardation, skeletal deformities (e.g., bowed legs, rachitic rosary), and delayed motor development. Dental abnormalities, hypocalcemia (leading to tetany or seizures), and alopecia may occur, particularly in type 2. Adults may present with osteomalacia and bone pain.

Diagnosis

Diagnosis involves blood tests to measure calcium, phosphate, alkaline phosphatase, and vitamin D metabolites (e.g., 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D). Genetic testing confirms mutations in CYP27B1 or VDR. Radiographs may show rachitic changes (e.g., widened growth plates, frayed metaphyses) or osteomalacia.

Treatment Options

Treatment focuses on correcting vitamin D deficiency and mineral imbalances. Type 1 responds to high-dose active vitamin D (calcitriol) or its analogs, while type 2 requires high-dose vitamin D (ergocalciferol or cholecalciferol) to bypass receptor defects. Calcium and phosphate supplements, along with dietary modifications, support bone health. Regular monitoring of serum levels is essential.

Prognosis and Follow-Up

Prognosis is generally good with early, consistent treatment, though skeletal deformities may persist. Lifelong therapy is often necessary to prevent relapse. Follow-up includes regular blood tests to monitor mineral levels, bone density assessments, and orthopedic evaluations for deformities. Growth and development are typically normalized with proper management.

Complications

Complications may include permanent skeletal deformities (e.g., bowing, short stature), chronic pain, and increased fracture risk. Untreated hypocalcemia can lead to seizures or cardiomyopathy. Delayed diagnosis may result in irreversible bone damage or growth impairment.

Lifestyle & Prevention

Lifestyle measures include adherence to prescribed vitamin D and mineral supplements, a balanced diet rich in calcium and phosphate, and regular weight-bearing exercise to support bone health. Sunlight exposure (with caution) may help, but supplementation is primary. Genetic counseling is recommended for families with a history of the disorder.

When to Seek Professional Help

Seek care if symptoms like bone pain, muscle weakness, or growth concerns arise, especially in children. Immediate medical attention is needed for signs of hypocalcemia (e.g., tetany, seizures) or severe deformities. Regular follow-up with an endocrinologist or geneticist is advised for ongoing management.

Tips for Medical Coders

Document the specific type (1 or 2) when available, as both are included in E83.32. Ensure clinical notes specify hereditary vitamin D-dependent rickets and confirm genetic or biochemical evidence supporting the diagnosis. Avoid using this code for non-hereditary or acquired vitamin D deficiencies.