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Crumbs homolog 2 (CRB2) is a protein involved in maintaining cell polarity and adhesion. Biallelic pathogenic variants in the CRB2 gene cause CRB2-related syndrome, characterized by a triad of congenital hydrocephalus, nephrotic syndrome, and elevated α-fetoprotein levels in maternal serum or amniotic fluid. However, the clinical phenotype varies widely, ranging from severe multisystem disease to isolated nephropathy.
We present a case of CRB2-related syndrome complicated by congenital hydrocephalus, congenital nephrotic syndrome, and schwannoma.
The patient is a 13-year-old girl. During the fetal period, ventriculomegaly, coarctation of the aorta (CoA), and atrial septal defect (ASD) were detected. She was delivered by cesarean section at 37 weeks of gestation, with a birth weight of 2,936 g. Soon after birth, she underwent surgical repair of CoA and ASD, as well as placement of a ventriculoperitoneal (V-P) shunt. At 11 months of age, routine urinalysis revealed proteinuria (3+) and hematuria (3+). A renal biopsy at 1 year of age showed focal segmental glomerulosclerosis (FSGS), perihilar variant. Since a congenital etiology was suspected, immunosuppressive therapy was considered ineffective, and she was managed conservatively with angiotensin-converting enzyme (ACE) inhibitor and angiotensin II receptor blocker (ARB). At 3 years old, she developed afebrile seizures, leading to a diagnosis of symptomatic epilepsy. She continued regular follow-up for seizures, proteinuria, and her cardiac condition. At around 10 years and 9 months, she began to experience progressive weakness in the lower limbs accompanied by hyperreflexia and pathological reflexes. As gait instability worsened, magnetic resonance imaging (MRI) of the cervical spine was performed at 11 years and 5 months, revealing a tumor at the C2–C4 level compressing the spinal cord, and no other lesions were identified. Surgical resection was performed at 11 years and 6 months, and the tumor was diagnosed as a schwannoma. Following the discovery of this tumor, the patient’s parents requested genetic testing. A targeted next-generation sequencing panel for congenital nephrotic syndrome revealed compound heterozygous pathogenic variants in the CRB2 gene. Throughout her clinical course, she had persistent proteinuria (3.0 g/g·Cr) and hematuria (2+). Renal ultrasound and MRI showed normal kidney morphology without cystic changes.
To our knowledge, this is the first reported case of CRB2-related syndrome complicated by schwannoma. Further accumulation and analysis of similar cases will be essential to elucidate the potential role of CRB2 in neural and renal development, as well as in tumorigenesis. Moreover, CRB2-related syndrome should be considered in cases presenting with congenital hydrocephalus and proteinuric kidney disease in early childhood.
