Discovery of novel gene mutations associated with nephrotic syndrome in children

Researchers have identified gene mutations linked to deficient filtering of the blood by the kidney, thus leading to high levels of urinary protein excretion.

By Diego Freire  |  Agência FAPESP – Nephrotic syndrome, a cluster of symptoms of kidney disease mainly evidenced by excessive urinary excretion of protein, has several causes, including genetic mutations that are not yet fully understood. Researchers at the University of Campinas (UNICAMP) in São Paulo State, Brazil, have identified novel mutations in some of the genes associated with the syndrome, paving the way for more accurate diagnosis and treatment of kidney disease.

Their assessment of the frequency and distribution of these mutations is unprecedented in Brazil and was performed under the aegis of the research project “Whole exome sequencing in Brazilian children and adolescents with steroid resistant nephrotic syndrome”.

“Our aim is to contribute to the establishment of a molecular basis for the disease in the Brazilian population,” said Mara Sanches Guaragna, a researcher at UNICAMP’s Center for Molecular Biology & Genetic Engineering (CBMEG). “With this knowledge, it will be possible to conduct molecular analysis of specific groups of children with nephrotic syndrome, potentially enabling these patients to receive personalized treatment. For example, it should be possible to identify patients for whom a kidney transplant from a living donor is suitable, with a relatively low risk of relapse.”

According to Guaragna, nephrotic syndrome is one of the leading childhood kidney disorders. The syndrome is characterized by high levels of urinary protein excretion, a condition known as proteinuria, in addition to hypoalbuminemia, a deficit of albumin in the blood. Albumin deficiency allows fluid to move from the blood vessels into the tissues, thus resulting in edema. The condition also includes hyperlipidemia, an abnormally high concentration of fats in the blood.

The disease is caused by malfunctioning of the glomeruli, networks of capillary blood vessels that filter blood in the kidney and allow metabolic waste to be excreted in the urine.

“People who suffer from nephrotic syndrome can be classified as either corticosensitive, meaning they respond to treatment with corticoids, or corticoresistant,” Guaragna said. “We know there’s a structural problem in corticoresistant patients with mutations. In these cases of proven genetic origin, withdrawing treatment with corticoids can be considered in order to avoid all the adverse effects of drugs that depress the immune system.”

Novel mutations

After analyzing the distribution of mutations in a group of 150 Brazilian children and adolescents with nephrotic syndrome, the researchers identified a novel mutation in each of the key genes associated with the symptoms: NPHS1, NPHS2, and WT1.

They then examined these genes’ exons, the parts that encode the proteins that must be expressed – in this case nephrin, podocin, and WT1 transcription factor – in order for the kidney to filter blood correctly. To do so, they had to “amplify” the genes by increasing the number of copies by using polymerase chain reaction. Amplification of the exons enabled them to identify the mutations.

The mutations identified by the researchers in the genes NPHS1 and NPHS2 have recessive inheritance, meaning that two mutant genes, one from the father and the other from the mother, are needed for the disease to develop. In the case of WT1, the mode of inheritance is dominant: the disease develops if only one of the genes is mutated.

“Having identified pathogenic mutations as the cause of the disease in the cases analyzed, we’re closer to discovering a frequent cause of nephrotic syndrome specifically in the population studied, although larger samples must be analyzed in order to produce more definitive epidemiological findings,” Guaragna said.

Today, nephrotic syndrome is diagnosed by means of urine tests showing the excretion of abnormally large amounts of protein or blood tests pointing to a deficiency of albumin. The physician may also prescribe a kidney biopsy, which is performed by removing a tissue sample from one of the patient’s kidneys to explore the possibility of glomerular dysfunction. A genetic test to identify mutations such as those recently discovered may also be requested if there are doubts about the need for a kidney transplant.

In addition to involving CBMEG, the study involved researchers at UNICAMP’s Kidney Center (CIN) and the same university’s Interdisciplinary Group for the Study of Sex Determination & Differentiation (GIEDDS).