Denys-Drash Syndrome (DDS)

Overview

Classic Triad

Genetics and Molecular Mechanism

• Gene: WT1, chromosome 11p13
• Mutation type: Dominant-negative missense mutation in the zinc-finger region of the WT1 protein
• This disrupts DNA-binding properties and interferes with the remaining wild-type allele
• The heterozygous mutation is sufficient to cause genitourinary abnormalities but not tumorigenesis alone
• Wilms tumors in DDS require biallelic inactivation of WT1 (i.e., a second hit is needed for tumor development)
• WT1 is expressed in the kidney and gonads during embryogenesis; it regulates glomerular podocyte-specific proteins and genes involved in renal differentiation

Renal Pathology

• Diffuse mesangial sclerosis (DMS) - the hallmark glomerular lesion
• Presents as congenital or infantile nephrotic syndrome (steroid-resistant)
• Rapidly progressive to end-stage renal disease (ESKD), often by age 3 years
• DMS is distinct from focal segmental glomerulosclerosis (FSGS), which characterizes the related Frasier syndrome

Gonadal Features

• Patients with 46,XY karyotype have gonadal dysgenesis with streak gonads and male pseudohermaphroditism - female or ambiguous external genitalia
• Mixed gonadal dysgenesis is common
• Gonadoblastoma risk: ~40% in DDS - streak gonads must be removed prophylactically
• Patients who reach ESKD may present phenotypically female but be genotypically XY

Wilms Tumor Features

• Risk approximately 90% (much higher than WAGR at ~33%)
• May be diagnosed before, simultaneously with, or after the nephropathy
• High incidence of bilateral Wilms tumor
• Favorable triphasic histology (blastemal, stromal, epithelial elements) is most common
• Risk of germ cell tumors (gonadoblastomas) is also increased due to disrupted gonadal development

DDS vs. Frasier Syndrome (Related WT1 Disorder)

Wilms Tumor Predisposition Syndromes Summary

Management

1. Nephrectomy - prophylactic bilateral nephrectomy has been used given the high Wilms tumor risk and to delay or manage ESKD
2. Wilms tumor treatment - surgery, chemotherapy (vincristine, actinomycin D), +/- radiotherapy per stage
3. Renal replacement therapy - dialysis and renal transplantation for ESKD
4. Gonadectomy - bilateral prophylactic removal of streak gonads due to ~40% gonadoblastoma risk
5. Gender assignment - in XY DSD cases, involves multi-disciplinary team; historically most raised female; decisions guided by anatomy and degree of virilization
6. Wilms tumor surveillance - abdominal ultrasound every 3 months until age 7 in WT1 mutation carriers

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 454
• Campbell Walsh Wein Urology (3-Volume Set), p. 1275
• Comprehensive Clinical Nephrology, 7th Edition
• Brenner and Rector's The Kidney, 2-Volume Set

WAGR Complex (WAGR Syndrome)

What Does WAGR Stand For?

Chromosomal Basis - Contiguous Gene Deletion Syndrome

Molecular Mechanism: Two-Hit Model

1. First hit - germline heterozygous deletion of one WT1 allele (constitutional, inherited or de novo)
2. Second hit - somatic nonsense or frameshift mutation in the remaining WT1 allele in a renal cell
3. This biallelic inactivation of WT1 triggers Wilms tumor formation

Clinical Features

1. Wilms Tumor (Nephroblastoma)

• Lifetime risk ~33% (lower than Denys-Drash syndrome's ~90%)
• Peak incidence age 2-5 years; 90% before age 4 in WAGR
• Can be bilateral (synchronous or metachronous)
• Belongs to the "type I Wilms tumor" subset: stromal-predominant favorable histology, intralobar nephrogenic rests, early onset, genitourinary anomalies in males

2. Aniridia

• Complete or partial absence of the iris
• Caused by PAX6 haploinsufficiency
• Associated with nystagmus, photophobia, reduced visual acuity, cataracts, glaucoma
• Aniridia alone (without WT1 deletion) does NOT predispose to Wilms tumor

3. Genitourinary Anomalies

• Cryptorchidism, hypospadias, streak gonads, renal anomalies
• Males are more severely affected
• Result from WT1 haploinsufficiency (WT1 is required for normal renal and gonadal embryogenesis)

4. Intellectual Disability / Developmental Delay

• Due to deletion of additional contiguous genes at 11p13 beyond WT1 and PAX6
• Variable in severity; generally mild to moderate
• The larger the deletion, the more severe the phenotype

WT1 Gene - Role in Development

• Encodes a zinc-finger transcription factor
• Critical for normal kidney and gonadal development
• Regulates mesenchymal-to-epithelial transition during nephrogenesis
• Required for ureteric bud outgrowth
• Knockout in mice results in complete failure of kidney and gonadal development
• Also regulates podocyte-specific proteins in glomeruli

Wilms Tumor Predisposition Syndromes - Comparison

Management

1. Wilms tumor surveillance - renal ultrasound every 3 months until age 8 (given high risk)
2. Ophthalmology - regular review for aniridia-related glaucoma, cataract
3. FISH/CMA testing - all children with aniridia should be screened for 11p13 deletion to identify those with WT1 co-deletion (i.e., WAGR vs. isolated PAX6 aniridia)
4. Developmental support - early intervention for intellectual disability
5. Nephrology follow-up - monitoring renal function (especially post-nephrectomy)
6. Wilms tumor treatment - surgery + chemotherapy per COG/SIOP protocols; prognosis is generally excellent with ~90% cure rates overall

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 453-454
• Campbell Walsh Wein Urology (3-Volume Set), p. 1600-1604
• Emery's Elements of Medical Genetics and Genomics, p. 192
• Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 1644

Von Hippel-Lindau (VHL) Syndrome

Overview

Genetics

Mutation Types and Genotype-Phenotype Correlation

Molecular Mechanism - The VHL/HIF Pathway

1. HIF-1α is hydroxylated by HIF prolyl hydroxylase (PHD) in the presence of oxygen
2. Hydroxylated HIF-1α is recognized and bound by the VHL protein
3. VHL is part of an E3 ubiquitin ligase complex (also containing elongins B and C)
4. This complex ubiquitinates HIF-1α, targeting it for proteasomal degradation
5. HIF levels remain low → no upregulation of angiogenic/growth genes

1. HIF-1α and HIF-2α cannot be ubiquitinated and degraded (even under normoxia)
2. HIF accumulates and enters the nucleus, dimerizing with HIF-β
3. The HIF-α/HIF-β complex drives transcription of target genes:
   • VEGF - vascular endothelial growth factor (angiogenesis)
   • PDGF - platelet-derived growth factor (mitogen)
   • GLUT1 and glycolytic enzymes (Warburg metabolism)
   • IGF-1 - insulin-like growth factor-1 (cell growth)
   • Erythropoietin - can cause paraneoplastic polycythemia
4. Result: constitutive "pseudo-hypoxic" state → uncontrolled angiogenesis and tumor growth

Clinical Manifestations

Major Tumor Types

Hemangioblastoma - Histology

• Highly vascular neoplasm
• Presents as a mural nodule within a large fluid-filled cyst
• Microscopically: numerous thin-walled capillary vessels separated by stromal cells with vacuolated, lipid-rich cytoplasm
• Stromal cells express inhibin (TGF-β family member) - useful diagnostic marker

Clear Cell RCC - Molecular Note

• In virtually all clear cell RCCs (sporadic, familial, or VHL-associated): deletion of one copy of chromosome 3p25 (VHL locus)
• In up to 80% of sporadic clear cell RCC: the second VHL copy is inactivated by somatic mutation or epigenetic silencing (hypermethylation)
• This confirms VHL as a classic two-hit tumor suppressor for this histologic subtype

VHL Syndrome Classification (Types)

Screening and Surveillance

Management

1. Renal tumors - active surveillance until tumor reaches 3 cm; then nephron-sparing surgery is preferred to preserve renal function (given bilateral/multifocal nature)
2. CNS hemangioblastomas - surgical resection for symptomatic lesions
3. Retinal angiomas - laser photocoagulation or cryotherapy
4. Pheochromocytoma - alpha-blockade first, then surgical excision
5. Targeted therapy - VHL loss → HIF overactivation → VEGF pathway is a key therapeutic target; agents such as belzutifan (HIF-2α inhibitor) are now approved specifically for VHL-related tumors

Comparison with Other Hereditary RCC Syndromes

• Robbins, Cotran & Kumar Pathologic Basis of Disease, pp. 453, 880
• Robbins & Kumar Basic Pathology, p. 866
• Campbell Walsh Wein Urology (3-Volume Set), pp. 2849-2850
• Quick Compendium of Clinical Pathology, 5th ed., p. 408

Dietl's Crisis

Definition

Pathophysiology

1. High fluid intake or diuretics → brisk diuresis → rapid increase in urine flow rate
2. Urine reaches the partially obstructed UPJ faster than it can drain into the ureter
3. Renal pelvis and calyces acutely distend → rise in intrapelvic pressure
4. This distension causes severe colicky flank pain
5. After a few hours, urine eventually overcomes the partial obstruction or backs up until voiding drives a large urinary output
6. The pelvis decompresses → pain resolves + large volume of urine is passed + the renal swelling visibly reduces

Causes of the Underlying UPJ Obstruction

Intrinsic (more common)

• Idiopathic UPJ stenosis - most common; aperistaltic/atretic segment with abnormal musculature
• Deficiency of c-KIT-positive interstitial pacemaker cells
• Increased collagen deposition replacing normal smooth muscle
• Mucosal folds or valves at the UPJ

Extrinsic

• Aberrant/accessory lower pole renal artery - crosses and compresses the UPJ
• Adhesions
• Mobile/ptotic kidney (nephropexy) - historically considered a cause

Key Anatomic Points

• More common in males and on the left side
• Bilateral in 10-40% of cases
• Approximately 10% of UPJ obstruction patients also have vesicoureteral reflux (VUR)

Clinical Features

Investigations

During an Acute Episode (Most Informative)

• Renal ultrasound - best performed during the painful episode to capture acute dilatation of the renal pelvis and calyces without a dilated ureter (distinguishes UPJ from ureteral obstruction)

Between Episodes

MAG3 Lasix Renogram Interpretation

• Normal: T½max < 10-15 minutes
• Obstruction: T½max > 20 minutes after furosemide administration + rising curve
• Also provides split renal function (affected vs. contralateral kidney)
• Differential function < 40% on the affected side indicates significant obstruction
• Helps differentiate true obstruction from congenital ectasia (non-obstructed dilatation - does not need surgery)

Management

Conservative (Observation)

• Mild symptoms + good renal function + low-grade obstruction
• Monitor with serial ultrasound and renography

Decompression (Temporary/Emergency)

• Percutaneous nephrostomy tube - for acute obstructive uropathy or infected hydronephrosis
• Ureteral (DJ) stent insertion

Definitive Surgery - Pyeloplasty

• Symptomatic (Dietl's crises)
• Obstructive excretory curve on diuretic renography
• Renal function deterioration (>10% decrease in split function)
• Progressive hydronephrosis
• Recurrent UTI, stones

Techniques

• Overall long-term patency rate for pyeloplasty: > 90%
• A stent is left across the anastomosis; Foley catheter placed to prevent reflux during the renogram

Summary Table

• Campbell Walsh Wein Urology (3-Volume Set), pp. 521, 3199-3206
• Sabiston Textbook of Surgery, p. 134
• Comprehensive Clinical Nephrology, 7th Edition, p. 840
• Bailey & Love's Short Practice of Surgery, 28th Edition, p. 3484
• S. Das: A Manual on Clinical Surgery, 13th Edition, p. 4299

Potter Sequence (Potter Syndrome)

Terminology - Important Distinction

Pathogenesis

Why is amniotic fluid important?

• From the second trimester onward, fetal urine is the primary source of amniotic fluid
• Amniotic fluid provides:
  1. Mechanical cushion - protects against compression/deformity
  2. Lung development - fetal breathing movements of amniotic fluid are essential for bronchial branching and alveolar development

Consequences of oligohydramnios

Potter Facies (Classic Facial Appearance)

• Flattened/broad nose
• Retrognathia (receding chin)
• Low-set ears - severely malformed, bilateral
• Epicanthal folds (palpebronasal folds)
• Widely separated eyes
• Skin appears redundant and compressed

Causes of Potter Sequence

Bilateral Renal Agenesis - In Detail

Embryology

• Renal agenesis results when ureteric buds fail to develop from the mesonephric duct or degenerate early
• Without the ureteric bud, the metanephrogenic blastema receives no inductive signal → no nephron formation
• Failure of bud penetration → no kidney development
• Likely multifactorial causation; rarely biallelic variants in ITGA8 or GFRA1 reported
• Also theorized: complete in utero involution of polycystic kidneys → apparent agenesis with a blind-ending ureter

Epidemiology

• Incidence: ~1 in 3,000-10,000 births (varies by source)
• More common in males
• Usually sporadic; sibling recurrence risk ~3%, rising to 15-20% with a family history of agenesis
• 15% risk of congenital renal abnormalities in first-degree relatives of the index patient

Prenatal Diagnosis

• Antenatal ultrasound: oligohydramnios/anhydramnios + absent/non-visualized kidneys + contracted/non-visualized bladder (no urine produced)
• Fetal MRI can confirm the diagnosis

Clinical Features at Birth

Prenatal Management

Unilateral Renal Agenesis (Contrast)

• Occurs ~1 in 1000 neonates; males more affected; left kidney usually absent
• Usually asymptomatic - contralateral kidney undergoes compensatory hypertrophy
• Associated with single umbilical artery - should prompt investigation
• Long-term complications: hypertension, recurrent infection, renal insufficiency

Summary

• Robbins & Kumar Basic Pathology, p. 135
• The Developing Human: Clinically Oriented Embryology, p. 696
• Quick Compendium of Clinical Pathology, 5th ed.
• Comprehensive Clinical Nephrology, 7th Edition, p. 775
• Creasy & Resnik's Maternal-Fetal Medicine, p. 6130
• Emery's Elements of Medical Genetics and Genomics, p. 242
• Grainger & Allison's Diagnostic Radiology

Horseshoe Kidney

Definition

Epidemiology

Embryology and Pathogenesis

• During ascent from the pelvis, the developing metanephric kidney masses normally rotate medially and migrate cranially
• In HSK, the lower poles of the two metanephric masses fuse before the kidneys have completed rotation and ascent (at the 4-6 week stage)
• Further ascent is arrested when the isthmus becomes entrapped beneath the inferior mesenteric artery (IMA) as it arises from the aorta
• The isthmus typically lies at the level of L3-L4 vertebrae, just below the IMA origin

Why Does Rotation Fail?

• Because fusion occurs before rotation, the renal pelvis faces anteriorly (instead of medially) and the calyces point posteriorly and medially - the opposite of the normal orientation

Anatomy

Isthmus

• Located anterior to the aorta and inferior vena cava (rarely passes between or behind them)
• Usually bulky with functioning parenchyma and its own blood supply
• Sometimes just fibrous tissue
• Position: anterior to L3/L4, below the IMA, occasionally as low as the sacral promontory or true pelvis

Collecting System and Ureters

• Calyces are normal in number but atypically oriented - pointing posteriorly
• The lowermost calyces extend caudally/medially, may overlie the vertebral column
• Ureter inserts high on the renal pelvis and lies laterally (due to incomplete rotation)
• The ureter drapes ventrally over the renal isthmus (where it may be compressed by lower pole vessels) - this creates the risk of obstruction
• Lower ureter enters the bladder normally
• Occasionally associated with retrocaval ureter, ureteral ectopia, or duplication

Blood Supply - Highly Variable

• Only ~5-20% have a single artery to each moiety
• Usually multiple aberrant arteries from:
  • Aorta (above or below isthmus)
  • Inferior mesenteric artery
  • Common or external iliac arteries
  • Sacral arteries
• The isthmus itself may have separate arterial supply from the aorta
• This aberrant vasculature is a key consideration for surgery and PCNL

Clinical Features

Rovsing's Sign

• Abdominal pain, nausea, and vomiting upon hyperextension of the spine - occasionally described due to pressure on the isthmus against the aortic plexus

Complications and Associated Conditions

Urological Complications

Neoplastic Risk

Associated Syndromes and Congenital Anomalies

• Turner syndrome - HSK present in ~60% of females with Turner syndrome (45,X) - the most common association
• VACTERL association - anorectal malformations, vertebral/tracheoesophageal anomalies
• Neural tube defects - HSK in ~3% of these patients
• Caudal regression syndrome
• Genitourinary anomalies: hypospadias, undescended testes (4% of males), bicornuate uterus, septate vagina (7% of females)
• 50% of patients with HSK have at least one associated extrarenal anomaly

Imaging

Characteristic Imaging Signs

• "Drooping lily" / inverted V sign - renal axes
• Lower pole calyces pointing medially toward the spine
• Flower vase sign on IVU - overall HSK appearance

Management

Asymptomatic HSK

• No treatment required; most patients remain asymptomatic lifelong
• Follow-up if associated anomalies or risk factors

Complications

PCNL in Horseshoe Kidney

• Upper pole access is preferred - most posterior, lateral, often subcostal, and provides excellent access to the whole collecting system
• Lower pole calyces are usually not safely accessible by direct puncture
• Puncture is more medial than in normal kidneys; may pass through paraspinal musculature
• Pre-op CT/MRI mandatory to assess: aberrant vasculature, retro-renal colon (present in ~5/12 cases in one series), calyceal orientation

Summary Table

• Campbell Walsh Wein Urology (3-Volume Set), pp. 2934-2960
• Comprehensive Clinical Nephrology, 7th Edition, p. 784-795
• Bailey & Love's Short Practice of Surgery, 28th Edition, p. 3316-3327
• The Developing Human: Clinically Oriented Embryology, p. 697-698