Phenotypic manifestation of homozygous partial deletion of the chromosome 1 segment spanning CFHR3 region

This article presents two clinical cases of patients with a homozygous deletion of segment of chromosome 1, which covers regions of genes associated with complement factor H, in particular CFHR3. Patients underwent in-depth clinical studies, heredity assessment, laboratory, instrumental and genetic diagnostics. The first clinical case describes a clinical case with deleted chromosome 1 segment in a 9-year-old girl who was diagnosed with atypical hemolytic-uremic syndrome. This is a complement-dependent disease that affects both adults and children. It is known that a defect in any proteins included in the alternative complement activation pathway can lead to atypical hemolytic-uremic syndrome. However, this syndrome is most often caused by defects in chromosome 1 region, including gene sequences associated with complement factor H – CFHR1 and CFHR3. Modern treatment of atypical hemolytic uremic syndrome involves targeted pathogenetic treatment, therefore, the genetic diagnosis seems to be a necessary step for differential diagnosis and confirmation. The patient had fairly typical clinical symptoms, including signs of thrombotic microangiopathy, thrombocytopenia, hemolytic anemia and increasing renal failure. It is also known that her mother had congenital hydronephrosis, and the pregnancy proceeded against a background of ureaplasma, mycoplasma, cytomegalovirus infection, chronic pyelonephritis, and preeclampsia.

The second clinical case of a deleted chromosome 1 region, involving the CFHR3 gene, is a description of the disease in a boy of 8 years old, while the disease manifested with alopecia at the age of 4. Intermittent alopecia was the main symptom, while there were no signs of renal failure, thrombocytopenic purpura, and other symptoms characteristic of atypical hemolytic-uremic syndrome. The boy also revealed some congenital defects of the urinary system: bladder diverticulum, unilateral ureterohydronephrosis, and bilateral dilatation of the pyelocaliceal system. The detected genetic defect is usually associated with atypical hemolytic uremic syndrome. However, the phenotype, i.e., clinical manifestations, determined a completely different diagnosis – primary immunodeficiency, a group of complement defects, and a deficiency of complement factor H-related protein. After analyzing the given clinical cases, we can conclude that clinical manifestations may vary significantly in carriers of same gene mutations. This suggests that there are additional factors (genetic or environmental) that can influence the formation of various phenotypic manifestations of this pathology.

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