1. INBORN ERRORS OF METABOLISM
9th International pCRRT Conference on Pediatric Continuous Renal Replacement Therapy
August 31-September 2, 2017
Disney’s Yacht & Beach Club Resorts. Lake Buena Vista, Florida
INBORN ERRORS OF METABOLISM
Stefano Picca, MD
ISN Educational Ambassador
Dept. of Pediatrics, Dialysis Unit
“Bambino Gesù” Pediatric Research Hospital ROMA, Italy

2. OUTLINE
HYPERAMMONEMIA
OXALOSIS

3. BACKGROUND #1: IEM TOXIN CHARACTERISTICS
•All IEM toxic compounds: small, non-protein bound molecules , relatively small distribution volume
Best cleared by diffusion
High to very high generation rate → high clearances needed
Many patients are neonates (complex clinical management)

4. IEM DIALYZABLE TOXINS DISTRIBUTION
BACKGROUND #2:
IEM DIALYZABLE TOXINS DISTRIBUTION
Usually in acute patients (UCD, OA):
Solute is distributed in a known volume , more or less bound to proteins in a stable physico-chemical condition
→ FIRST ORDER KINETICS
Usually in chronic patients (Oxalosis):
Solute undergoes variable physico-chemical changes causing its reversible accumulation
→ COMPLEX KINETICS

5. KEY POINTS OF NEONATAL HYPERAMMONEMIA
Extremely neurotoxic (per se or through intracellular excess glutamine formation) → astrocyte swelling, brain edema, coma, death or severe disability
thus:
emergency treatment has to be started even before having a precise diagnosis since prognosis may depend on a number of factors

6. PROGNOSTIC INDICATORS IN DIALYZED AND NON-DIALYZED NEONATES: SURVIVAL
pNH4 level
Dialysis efficiency
Timing of intervention
Enns
2008
Early metabolic defect diagnosis
Bachmann
2003
Initial pNH4 <300 mol/L
Peak pNH4 <480 mol/L
McBryde, 2006
pNH4 at admission<180 mol/L
Time to RRT<24 hrs
Medical treatment<24 hrs
BP> 5%ile at RRT initiation
HD initial RRT (trend)
Schaefer,
1999
50% pNH4 decay time < 7 hrs
(catheter > 5F)
Picca,
2001
pre-treatment coma duration < 33 hrs (no influence of post-treatment duration)
responsiveness to pharmacological therapy
Pela,
pre-treatment coma duration < 10 hrs

7. VC Ke G KC KD PLASMA NH4 (DIS)EQUILIBRIUM Ana/Catabolism
Defect severity/phenotype
Different starting conditions
Different previous medical therapy G VC KC Ke KD
Modified from Sargent JA, Gotch FA, 1996

8. AMMONIUM CLEARANCE AND FILTRATION FRACTION USING DIFFERENT DIALYSIS MODALITIES
Patient
(n)
Type of
Dialysis Qb
(ml/min) Qd
Ammonium Clearance (ml/min/kg)
Ammonium Filtration Fraction (%) 3
CAVHD
10-20
8.3
(0.5 l/h)
CVVHD
20-40
(2-5 l/h) 2 HD
10-15
500
Picca et al., 2001
Patient (n)
Type of Dialysis
Ammonium Clearance (ml/min) 4 PD
(1.4±1.1,
about ml/min/kg)
Arbeiter et al., 2009

12. CONCLUSIONS- RRT in HYPERAMMONEMIA
RRT induces rapid decrease of ammonium levels
Four hours seem a reasonable time for pharmacological treatment before RRT initiation
HD/CVVHD with high dialysate flow seem the best available options
However, PD induces similar plasma ammonium decay in the face of lower ammonium clearance (glucose utilization → anabolism? Negative nitrogen balance → decreased ammonium generation rate? Better expertise with PD in neonates? -Bunchman shorter predialysis coma duration? –Picca 2015-)
Severe hyperammonemia can be reversed also by pharmacological treatment alone. Response to dialysis can be useless if coma duration before treatment is too long

13. KEY POINTS OF OXALOSIS •
Accumulation of insoluble oxalate in bone, kidney, heart and liver occurring in hyperoxaluria type 1 (PH1), a rare autosomal recessive disorder (1:120,000 live births) caused by the defect of liver-specific peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT)
In early expressed phenotype, oxalosis can lead to ESRD even in neonatal age
In these patients, combined liver-kidney transplantation is presently the therapeutic gold standard
No form of chronic dialysis is recommended in oxalosis but dialysis is needed:
awaiting transplantation
when small patient size does not allow transplantation or Tx not available
right after combined transplantation to prevent oxalosis relapse •
Cochat, modified

14. Oxalate mass balance in oxalosis
Not a single-pool model! G2
So, dialysis has to be established in order to correct uremia, but also in the attempt to remove Ox. In the meantime, a second clearance takes place, a sort of endogenous clearance with peripheral stores like…. G1 C C V K ● ●
Oxalosis
- bones - heart - peripheral nerves - joints - skin, soft tissues, retina…

15. From Marangella M et al, 1992

16. Pt #1: CURVILINEAR INTERDIALYSIS pOXALATE INCREASE
CVVHD
CVVHD
CVVHD
CVVHD
220
R2 = 0.988
R2 = 0.980
180
200
160
180
La courbe de meilleur ajustement n’est pas linéaire mais c’est justement une courbe
140
160
pOxalate ( m
mol/l)
mol/l)
140
120 m
2 =57.1
Y0 = ± 11.4
A1 = ± 32
T1 = 7.18 ± 1.72
120
2 =37.68
Y0 = ± 8.99
A1 = ± 60.6
T1 = 6.77 ± 1.53
100
100 80
pOxalate ( 80 60 60 40 40 20 20 6 6 12 18 6
5/0 5 10 15 20
TIME (hrs)
TIME (hrs)

17. Pt #1: HD plasma OXALATE KINETICS. Oxalate Generation Rate
CVVHD
CVVHD
CVVHD
CVVHD
220
180
200
160
180
G rate was calculated by the regression line of the first 6 hours after HD completion…
140
160
mol/l)
mol/l)
140
120 m
120
y= 13.9x
p= 0.017
y= 19.5x
p<
100 m
100 80
pOxalate (
pOxalate ( 80 60 60 40 40 20 20 5 15 15 6 6 12 18 6
5/0
TIME (hrs)
TIME (hrs)

18. Clinical characteristics, Genetics and Outcome
Pts
Sex
Age, BW
Oxalosis onset
Genetics
Dialysis start
Piridoxine
Peripheral stores
Age of Tx
Outcome
(present) 1 F SD
2 mos, 4.4 Kg anuric
Mut/var32delC (exon1);
IVS10 1G>t (intron 9)
5 mos
100mg/day
Bone
Retina
Heart ?
36 mos
L-K Tx
Grafts functioning 2 M KS
6 mos, 6.1 kg
anuric
Point Mut. c.603C>A (exone 6)
6 mos -
30 mos
Kidney primary non functioning 3 NK
6.5 yy, 20 Kg
pIle244hr/
pVal326Tyrfs
6.5 yy
7 yy
Grafts
functioning 4 MA
4 mos, 5,8 Kg
Subs. VS2-1 G-C (intron1); subs.ATA-ATG
(exone 10)
4 mos
5.1yy,
L-Tx;
5.9 yy
K-Tx 5 GN
8 mos, 6,7Kg
Anuric
c.416_418delTGG (exone 3);
c508>a (exone 4)
8 mos
80 mg/day
18 mos
L Tx
Awating
K Tx
Graft 6 RE
3,5 yy, 9.8 Kg
150mg/day
Nails
2.11yy,
K-Tx;
3.11yy
Died.
Post-tx hemorrhage

19. Characteristics of Dialysis
Pts
Dialysis
modality
Acces Qb
ml/min Qd
Dialysis schedule
Membrane m2
Dry Weight kg
Nocturnal PD, hours 1
CVVHD
Tunneled CVC in IJV (Quinton 28 cm) 34
300/h
6 h x 7day/week
Hemophan
0.22 m2
6,2 - 2
PD (1 mos) + HD
Peritoneal 60
500
APD
5 h x 6 day/week
PAN 0.3 m2
6.1
7.7
9 hours 3
PD (4 mos)
Tunneled CVC in IJV (Quinton 36 cm
150
5 h x 7 day/week
PS 0.4 m2 20 4 PD
Tunneled CVC in IJV
(Tesio)
4 h x 6 day/week
11.8
14 hours 5
(Quinton 28 cm)
7.2 6
PD (14 mos)
peritoneal
HD (from 14th month on)
Tunneled CVC in LSV
100
4 h x 3-4 day/week
9.8

20. TD = (G * V * 24) – Mass Removal
CALCULATIONS
V = Mass Removal
(Cpre – Cpost) + (G * Td)
G = Cpost + t – Cpost t
TD = (G * V * 24) – Mass Removal
Transfert de masse…
V: Ox distribution volume (L)
Cpre Cpost: Ox concentration pre and post HD (mol/L)
Tid: HD duration (hrs)
Ct: Ox concentration at t(hrs) after HD session end
G: Ox generation rate (mol/L per hour)
TD: tissue deposition rate (mol/24 h)
Adapted from Marangella, Yamauchi

21. OXALATE KINETICS in SIX CHILDREN ON CHRONIC HEMODIALYSIS
Pre-HD pOx
(mol/l)
181 ± 65
Generation Rate
(mol/l/h)
7.1 ± 4.6
Distribution Volume,
(% of BW)
59.1 ± 5.6
Tissue Deposition,
(mol/24h/kg)
15.4 ± 6.1
Oxalate clearance
(l/week/1.73 m2)
178 ± 21

23. Intensive dialysis can limit oxalate deposition
Patient #1: migration of a single translucent band
Bandes translucides…
6 months
12 months
16 months
18 months

25. 1) Estimating quantity of tissue deposition of oxalate
esempio di stima della percentuale di deposizione tissutale (A/B). A: area compresa tra la retta di generazione teorica e la reale concentrazione dell’ossalato; B: area di generazione dell’ossalato. Retta arancione: generazione teorica dell’ossalato; retta rossa: concentrazione reale dell’ossalato.
dopo esclusione del rebound post-dialitico, assumendo le tre ore post-dialitiche come espressione della generazione (G) epatica di ossalato, dove: G= a*x+b abbiamo ipotizzato che la differenza calcolata tra la generazione teorica (rettilinea) dell’ossalato e la concentrazione media reale (curva dello splay) rappresenti la quota di deposizione periferica dell’ossalato

26. 2) Estimating quantity of tissue deposition of oxalate
Stima della percentuale di deposizione di ossalato in base ai valori di ossalemia, calcolata nei nostri pazienti.
elaborando i nostri dati, secondo un modello logistico, abbiamo calcolato la ipotetica percentuale di deposizione dell’ossalato in base ai valori dell’ossalemia. Otteniamo una curva bifasica in cui, per valori di ossalemia inferiori a 50 µmol/l la percentuale di deposito è intorno allo 0%. E’ interessante notare che il valore di 50 µmol/L è tradizionalmente indicato come quello al di sotto del quale la probabilità di deposizione dell’ossalato scende a zero (26). Per valori superiori, la percentuale di deposizione aumenta fino a raggiungere l’ 80% quando l’ossalemia è maggiore di 200 µmol/l

27. 8 h hemodialysis q48h

28. 4 h hemodialysis q24h

29. 2 h hemodialysis q12h

30. CONCLUSIONS- RRT in OXALOSIS
RRT may be needed under particular circumstances
Intensive dialysis regimens (daily extracorporeal and nocturnal PD) are recommended
High frequency is more important than high efficiency
Oxalate kinetics provides evidence that oxalate generation rate is more severe in children than in adults

31. ACKNOWLEDGEMENTS Bambino Gesù Children Hospital: •
Metabolic Unit: Carlo Dionisi-Vici, MD; Andrea Bartuli, MD; Gaetano Sabetta, MD
Clinical Biochemistry Lab: Cristiano Rizzo BSc, PhD; Anna Pastore BSc, PhD
NICU: all doctors and nurses
Dialysis Unit: Francesco Emma, MD, all doctors and nurses (thanks!) •
In Italy: •
SINP (Italian Society of Pediatric Nephrology)
All doctors from Pediatric Nephrology and NICUs of Genova, Milan, Turin, Padua, Florence, Naples, Bari.
In Turin •
Michele Petrarulo and Martino Marangella, MD for Ox determination and precious advices
Roberto Bonaudo, MD and Rosanna Coppo, MD for data about oxalosis pt #2 •
In USA •
Timothy E. Bunchman MD, for this opportunity. Thanks, Tim.

33. Dialysis Unit, “Bambino Gesù” Pediatric Hospital Roma, Italy.
Doctor:
S. Picca
Headnurse:
V. Bandinu
Nurses:
N. Avari
D. Ciullo
E. Iacoella
P. Lozzi
C. Pia
L. Stefani
Nurse Coordinator:
M. D’Agostino

34. PECULIARITIES OF TOXIN DEPURATION IN IEM
•All IEM toxic compounds are small, non-protein bound molecules with relatively small distribution volume
As such, they are best cleared by diffusion
All of them show a high to very high generation rate . So theoretically, high clearances are needed
Most of these patients are neonates. This complicates clinical management during dialysis

35. 0-4 HOURS MEDICAL TREATMENT IN NEONATAL HYPERAMMONEMIA
6000
4000
2000
1000
non-responders (dialysis)
pNH ( m mol/l)
responders (med. treatment alone)
750 4
500
250 4 8
HOURS
Picca, 2002