WT1 Gene Mutations Cause Specific Genetic Syndrome

The question asks to identify the gene responsible for autosomal dominant focal segmental glomerulosclerosis (FSGS) combined with abnormal genitalia, Wilm's tumour, and mental retardation. This specific combination of symptoms is characteristic of Denys-Drash syndrome.

Understanding Denys-Drash Syndrome

• Inheritance: Denys-Drash syndrome is typically inherited in an autosomal dominant pattern.
• Symptoms: It is characterized by a triad of conditions:
  • Progressive focal segmental glomerulosclerosis (FSGS) leading to kidney failure.
  • Abnormal genitalia (disorders of sexual development), often appearing as male pseudohermaphroditism in individuals with a 46,XY karyotype.
  • Wilm's tumour (nephroblastoma), a type of kidney cancer usually affecting young children.
• Other Features: Mental retardation can also be associated with this syndrome.

Role of the WT1 Gene

The WT1 gene (Wilms' tumor 1 gene) plays a crucial role in the development of the kidneys and the reproductive system. Mutations in the WT1 gene are the known cause of Denys-Drash syndrome.

• Mutations in WT1 disrupt its function as a transcription factor, affecting the expression of genes critical for urogenital development.
• These mutations lead to the characteristic features of the syndrome, including kidney abnormalities (FSGS), gonadal abnormalities (abnormal genitalia), and an increased risk of Wilm's tumour.
• While often associated with sporadic cases or autosomal dominant inheritance, the specific clinical presentation described points strongly towards WT1 mutations.

Evaluating Other Options

Let's briefly look at why the other options are less likely:

• INF2: Mutations in the INF2 gene are linked to certain forms of familial FSGS, but typically not the broader developmental abnormalities seen in Denys-Drash syndrome.
• LMX1B: Mutations in the LMX1B gene cause Nail-patella syndrome, which involves kidney disease (nephropathy) and skeletal abnormalities, but not the specific combination of Wilm's tumour and abnormal genitalia described.
• APOL1: While APOL1 gene variants are strongly associated with kidney disease, including FSGS, particularly in certain populations, they are not linked to Denys-Drash syndrome or the specific constellation of developmental defects mentioned in the question.

Therefore, mutations in the WT1 gene are the cause of focal segmental glomerulosclerosis associated with abnormal genitalia, Wilm's tumour, and mental retardation.