AKT · Endocrine/Lipids, metabolic & inheritedlow yield

Fanconi syndrome (renal tubular)

Generalised proximal renal tubular dysfunction → urinary wasting

Overview

Generalised dysfunction of the proximal renal tubule causing urinary loss of glucose, amino acids, phosphate, bicarbonate, potassium and uric acid — producing a normal-anion-gap (type 2 proximal renal tubular) acidosis, hypophosphataemic rickets/osteomalacia, glycosuria with normal blood glucose, and polyuria. Causes: inherited (cystinosis, Wilson's, tyrosinaemia, galactosaemia) and acquired (drugs e.g. tenofovir, heavy metals, myeloma). (The packet's exemplar — congenital Fanconi ANAEMIA with short stature/absent radius is a separate haematological condition on child health.)

Recognise

Polyuria/polydipsia, dehydration; growth failure and bone disease (hypophosphataemic rickets/osteomalacia) in children
Biochemistry: GLYCOSURIA with NORMAL blood glucose, aminoaciduria, phosphaturia (low phosphate), proximal (type 2) renal tubular acidosis (normal anion gap, hypokalaemia), uricosuria
Causes: cystinosis (children), Wilson's, drugs (tenofovir, ifosfamide, gentamicin), myeloma, heavy metals

Red flags

Severe metabolic acidosis/hypokalaemia/dehydration
Underlying cause needing treatment (myeloma, drug toxicity, Wilson's)

Differentials & how to tell them apart

Diabetes mellitusglycosuria but with HIGH blood glucose — Fanconi has glycosuria with NORMAL glucose

Distal (type 1) renal tubular acidosisinability to acidify urine, hypokalaemia, stones — but not the generalised proximal wasting

Fanconi ANAEMIAa different disease — congenital bone-marrow failure with short stature/absent radii (the discriminator exemplar) — on child health

Investigations

Urine: glycosuria (normal blood glucose), generalised aminoaciduria, phosphaturia; blood: low phosphate/potassium/bicarbonate (normal anion gap acidosis), low urate. Investigate the cause (drugs, myeloma screen, copper studies, cystine).

Management

Replace phosphate/bicarbonate/potassium/vitamin D + treat the underlying cause

1Recognise the proximal tubular wasting pattern (glycosuria with normal glucose, aminoaciduria, phosphaturia, normal-anion-gap acidosis). Replace the losses and identify the cause.Gate: Glycosuria with a NORMAL blood glucose is the tell (not diabetes); always find the cause — a drug (tenofovir), myeloma, Wilson's or cystinosis — and treat it; do not confuse with Fanconi ANAEMIA (congenital marrow failure, short radius)
2Long-term electrolyte/vitamin D replacement; treat the cause (cysteamine for cystinosis, copper chelation for Wilson's, stop drug, treat myeloma).

Replace losses (phosphate, bicarbonate, potassium, vitamin D) — supportive correction of the tubular wasting

Treat the underlying cause — stop the offending drug; treat Wilson's/myeloma/cystinosis (cysteamine)

Key points

Glycosuria with NORMAL glucose + aminoaciduria + phosphaturia + normal-anion-gap acidosis = renal Fanconi syndrome. Find the cause. Don't conflate it with Fanconi ANAEMIA (the short-stature/absent-radius marrow-failure exemplar on child health).

Monitor & prognosis

Electrolytes, phosphate, bicarbonate, growth; cause.

Depends on the underlying cause.

Source: StatPearls; cross-ref child_health (Fanconi anaemia)