Renal

Question 1

Congenital causes of Fanconi Syndrome

Answer 1

Cystinosis (most common)
- Exam clue: common in Caucasians - blonde, blue eyes
Glycogen storage disorders
Galactosaemia
Fructose intolerance

Question 2

Clinical features of Fanconi Syndrome

Answer 2

Proximal tubular dysfunction:

1. Aminoaciduria, glycosuria, proteinuria (not albumin, tubular protein)
2. Acidemia (normal AG metabolic acidosis)
   - Urinary pH - initially alkalotic, then <5.5 (distal tubule can still excrete)
3. Hypophosphataemia - rickets
4. Hypocalcaemia - constipation, generalised muscle weakness
5. Hypokalemia
6. FTT, polyuria and polydipsia, growth retardation

Question 3

Constituents of the glomerular filtration barrier (3)

Answer 3

1. Capillary endothelial cells (fenestrations)
   - Allows free passage to water, solutes and proteins
   - Cells are too large to fit through pores
2. Glomerular basement membrane
   - Lamina rara interna - fused to capillary endothelial layer
   - Lamina densa
   - Lamina rara externa - fused to podocytes
   - BM carriers a net negative charge - repels proteins which also carry a negative charge
3. Filtration slit diaphragm between podocyte foot processes
   - Prevents proteins and other large molecules from entering Bowman’s space

Question 4

Why is creatinine clearance less accurate compared to inulin clearance when estimating GFR?

Answer 4

Creatinine is produced and excreted constantly, It is filtered freely from the glomerulus and it is not reabsorbed by the tubules, but it is secreted in the PCT. Therefore, it overestimates GFR by 10-20%.

*Creatinine is derived from creatine breakdown in skeletal muscle. It is secreted by the organic acid transporters in PCT.