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G6PD deficiency in Hong Kong: diversity and clinical relevance

G6PD deficiency in Hong Kong: diversity and clinical relevance. Dr Edmond S K Ma Division of Haematology Department of Pathology The University of Hong Kong. Acknowledgements. Dr Veronica Lam Department of Biochemistry HKU Dr W Y Au Department of Medicine QMH. Metabolic role of G6PD.

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G6PD deficiency in Hong Kong: diversity and clinical relevance

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  1. G6PD deficiency in Hong Kong: diversity and clinical relevance Dr Edmond S K Ma Division of Haematology Department of Pathology The University of Hong Kong

  2. Acknowledgements • Dr Veronica Lam • Department of Biochemistry HKU • Dr W Y Au • Department of Medicine QMH

  3. Metabolic role of G6PD • Detoxification of H2O2 • glutathione • catalase • Cell growth • redox regulation • J Biol Chem 273: 10609 - 17, 1998

  4. Prevalence of G6PD deficiency on neonatal screening in HK Males 4.47 % (n = 223,696) Females 0.27 % (n = 208,457) Data from Lo KK et al: Neonatal screening for G6PD deficiency in Hong Kong. In Lam STS, Pang CCD (eds): Neonatal and Perinatal Screening - the Asian Perspective, CUHK press, 1996, pp 33 - 35.

  5. Manifestations of G6PD deficiency • Drug-induced haemolytic anaemia • Infection-induced haemolysis • Favism • Neonatal jaundice • Chronic ‘non-spherocytic’ haemolytic anaemia (CNSHA)

  6. G6PD deficiency and NNJ in males: Asian Perspective LocationPrevalence ofPrevalence of NNJPrevalence of G6PD G6PD deficiencyamong G6PD deficientdeficiency among subjectsNNJ patients China/HK 3.6 % NA 15 - 30 % Thailand 7.5 % 30 % 30 - 60 % Malaysia/ 1.3 % 20 % NA Singapore References: 1. Lai HC, Lai MPY, Leung KS. J Clin Pathol 21: 44, 1968. 2. Lu TC, Wei H, Blackwell RQ. Pediatrics 37: 994, 1966. 3. Flatz G, Sringam S, Premyothin C, Penbharkkul S, Ketusingh R, Chulajata R. Arch Dis Child 38: 566, 1963. 4. Phornphutkul C, Whitaker JA, Worathumrong N. Clin Pediatr 8: 275, 1969. 5. Vella F. Experientia 17: 181, 1961. 6. Lie-Injo LE, Virjk HK, Lim PW, Lie AK, Ganesan J. Acta Haematol 58: 152, 1977.

  7. Diagnosis of G6PD deficiency • Screening test: Fluorescent spot test • G6PD assay • based on reduction of NADP as measured spectrophotometrically at 340 nm when haemolysate is incubated with G6P • caveats: reticulocytosis and recent blood transfusion • reference range: 6.35 - 10.33 IU/gHb • Review of blood film during acute haemolytic episode

  8. G6PD haemolysis

  9. Distribution of G6PD gene mutations • G6PD gene: • Maps to Xq28 • Spans 18 kb and consists of 13 exons (first exon is non-coding) • Active enzyme: either 2 or 4 identical subunits, each 59 kDa • Primary sequence of 515 amino acid

  10. Classification of G6PD variants Most of the 127 different mutations identified to-date are classified from Class I to Class IV (WHO classification) according to the severity / type of clinical manifestations: • Class I severe enzyme deficiency resulting in chronic non-spherocytic haemolytic anaemia (CNSHA) • Class II severe enzyme deficiency with (< 10% of the normal activity) • Class III mild to moderate enzyme deficiency (10 - 60% of normal activity) • Class IV very mild enzyme deficiency or almost normal enzyme activity (> 60% normal activity and no clinical problem)

  11. The types of mutation that cause G6PD deficiency Type of mutationNumber Single missense 111 Double or triple missense 8 Small in frame deletions 8 Splice site 3’ intron 10 1 (G6PD Vansdorf) Nonsense (female heterozygote) 1 (G6PD Georgia 1284 CA) Total 129 Note: Maternally transmitted severe G6PD deficiency is embryonic lethal. Longo L et al. The EMBO journal 16: 4229 – 4239, 2002

  12. G6PD mutations: relationship to structural domains

  13. G6PD structure Dimeric structure

  14. Distribution of G6PD mutations in South ChinaBased on Zuo L, Chen E, Du CS et al, Blood 76: 51a, 1990 (suppl) MutantNumber (total n =20) Canton 1376 GT 10 Kaiping (Anant) 1388 GA 5 Gaohe 95 AG 2 Viangchan 871 GA 2 Fushan 1004 CA 1

  15. Distribution of G6PD mutations in TaiwanHuang C-S et al. Am J Hematol 51: 19 - 25, 1996 Prevalence based on neonatal screening Sex No. screenedNo. deficient% Male 4,277 112 2.6 Female 3,771 50 1.3

  16. Distribution of G6PD mutations in TaiwanHuang C-S et al. Am J Hematol 51: 19 - 25, 1996 Variant Males (n = 102) Females (n = 43) Canton 1376 GT 50% 44% Kaiping 1388 GA 16.1% 18% ‘Chinese-3’ 493 AG 8% 12% ‘Chinese-5’ 1024 CT 6.2% 6% Gaohe 95 AG 5.4% 6% ‘Chinese-4’ 392 GT 1.8% Mahidol 487 GA 1.8% Viangchan 871 GA 0.9% Union 1360 CT 0.9%

  17. G6PD variants in Malaysian ChineseAinoon et al, Human Mutation 14: 352, 1999

  18. G6PD variants in Malaysian Malays Ainoon et al, Human Mutation 21: 101, 2003

  19. G6PD deficiency in Chinese males • Case accrued from 1996 - 2002 • Based on dubious or abnormal FST • Mutation detection: ARMS  sequencing • Among 139 samples collected • G6PD Kaiping (1388) 46 (33%) • G6PD Canton (1376) 40 (29%) • G6PD Goahe (95) 14 (10%) • G6PD Viangchan (871) 9 (6.5%) • G6PD Chinese-4 (392) 7 (5%) • G6PD Union (1360) 4 (3%) • G6PD Chinese-5 (1024) 2 (1.5%) • Unknown 9 (6.5%) • Poor DNA quality 8 (5.5%)

  20. G6PD deficiency in Chinese males Variant NumberG6PD activity (IU/gHb) Mean  SE Range 1388 (Kaiping) 43 0.90  0.23 0 - 8.6 1376 (Canton) 40 0.43  0.09 0 - 3.3 95 (Gaohe) 14 0.60  0.19 0 - 2.36 871 (Viangchan) 9 0.42  0.12 0.02 - 1.03 392 (Chinese-4) 7 1.05  0.19 0.18 - 1.82 1360 (Union) 4 0.22  0.13 0.045 - 0.6 1024 (Chinese-5) 2 1.95 (mean) 1.5 & 2.4

  21. Indications for G6PD screen: males IndicationNumber Haematological disorder 33 Routine 28 Jaundice and/or anaemia 25 BMT donor 13 Neonatal jaundice 11 Cerebral palsy, dyskinesia/dystonia 6 Known history of G6PD deficiency 3 Unknown 20

  22. G6PD deficiency in Chinese females • Case accrued from 1996 - 2002 • Based on dubious or abnormal FST • Among 42 samples collected • Heterozygous for G6PD Canton (1376) 16 (38%) • Heterozygous for G6PD Kaiping (1388) 7 (17%) • Heterozygous for G6PD Viangchan (871) 5 (12%) • Heterozygous for G6PD Goahe (95) 5 (12%) • Homozygous for G6PD Canton (1376) 1 (2.5%) • Compound heterozygous for 1376 and 392 1 (2.5%) • Unknown 4 (9%) • Poor DNA quality 3 (7%)

  23. G6PD deficiency in heterozygous females Variant NumberG6PD activity (IU/gHb) Mean  SE Range 1376 (Canton) 16 3.19  0.82 0.29 - 9.3 1388 (Kaiping) 7 4.94  0.48 3.05 - 6.37 871 (Viangchan) 5 2.88  0.77 0.29 - 4.98 95 (Gaohe) 5 5.20  1.89 0.6 - 12.1

  24. Indications for G6PD screen: females IndicationNumber Routine 14 Haematological disorder 11 Jaundice and/or anaemia 5 Neonatal jaundice 1 Cerebral palsy, dyskinesia/dystonia 1 Known history of G6PD deficiency 1 Unknown 9

  25. Conclusions • Spectrum of G6PD variants are similar to Chinese elsewhere • 3 commonest variants Canton, Kaiping and Gaohe accounts for 70 - 80% of cases • No class I variants encountered • G6PD Chinese-3 or Taipei (493 A G) while 9.3% in Taiwan, not seen in HK • Most diagnosed on routine screening, few (6) presented as haemolysis

  26. Conclusions • Female heterozygotes • Range of enzyme activity? • Normal enzyme level does not exclude heterozygosity • Males hemizygotes • G6PD Chinese-4 and Chinese-5 appear to show higher activity

  27. F/61 Complained of fever, chills and rigors Took Chinese herbs Prescribed nitrofurantoin by GP Admitted for jaundice Hb 11.4 g/dL (no retic %) WBC 17.1 X 109/L Plt 193 X 109/L Bilirubin 155 mmol/L (unconjugated) Haptoglobin <0.05 g/L Methaemalbumin 0.1 mg/dL Direct Coombs’ test negative Hb pattern normal G6PD: FST abnormal; assay 1.67 IU/gHb (normal range: 6.35 - 10.33 IU/gHb) Urine culture: E. coli USG liver: no cholangitic changes or gallstones G6PD haemolysis in female

  28. Acute haemolysis in G6PD deficiency

  29. G6PD haemolysis in female • Clinical progress • Fever and neutrophilia down with levofloxacin • Jaundice subsided • Heterozygous carrier of G6PD Canton • Family study • Son (M/29): G6PD enzyme level 0.28 IU/gHb • Confirmed G6PD Canton • Daughter (F/31): G6PD enzyme level 5.5 IU/gHb • Confirmed G6PD Canton heterozygote

  30. G6PD deficiency in females • Compound heterozygous or homozygous • XO • Clonal haemopoiesis • Extreme Lyonization

  31. Distribution of X-inactivation pattern from peripheral blood of normal females in 3 age groups (Gale RE et al, BJH 98: 512-9, 1997)

  32. G6PD deficiency in elderly females • 132 elderly females screened for G6PD deficiency • Median age: 80 years (range: 71 - 101) • G6PD deficiency = 7 (5.3%) • Median enzyme activity = 1.57 IU/gHb (range 0.51 - 4.73) • G6PD variant: • Canton = 2; Kaiping = 2; Goahe = 2; • Canton + 871 = 1 • 160 female BMT donors • Median age: 32 years (range: 15 - 58) • No G6PD deficiency identified

  33. Prevalence of G6PD deficiency on neonatal screening in HK Males 4.47 % (n = 223,696) Females 0.27 % (n = 208,457) Data from Lo KK et al: Neonatal screening for G6PD deficiency in Hong Kong. In Lam STS, Pang CCD (eds): Neonatal and Perinatal Screening - the Asian Perspective, CUHK press, 1996, pp 33 - 35.

  34. Hardy-Weinberg Law • Take • gene frequency of normal allele (p) = 95.53% • gene frequency of mutant allele (q) = 4.47% • Proportion of females • homozygous normal (p2) = 91.26% • heterozygous (2pq) = 8.54% • homozygous mutant (q2) = 0.2% • note: prevalence in female = 0.27% on neonatal screening

  35. HUMARA assay • Conventional • DNA amplification by primers targeting CAG repeats with or without digestion with HhaI or HpaII (methylation sensitive restriction enzyme) • HUMARA methylation specific PCR (MSP) • Chemical modification by sodium bisulfite • unmethylated cytosine  uracil • methylated cytosine unchanged • PCR amplification • Gel electrophoresis and product detection

  36. First exon HUMARA assay and HUMARA-MSP

  37. Normal young female Pre Hpa-II Ratio areas* A/A+B=52.3% A B Post Hpa-II Ratio areas A/A+B = 45.3% A B Digestion completion control Dde1 93% digested Humara A and B alleles heterozgyous polymorphic repeats *note stuttering

  38. CML case A B Pre-Hpa-II A/A+B=53.5% B Post-Hpa-II A/A+B = 8.3% A Dde1 94% digested Humara A and B alleles

  39. Elderly female A B Pre-Hpa-II * A/A+B=59.0% i.e. :overamplification of A allele by 1.4 times A B Post-Hpa-II* A/A+B = 88.4% Corrected for overamplification = 88.4/(88.4+11.6x1.4)=82.3% *corrected for stuttering of B allele into A area XE169 >95% digested Humara A and B alleles

  40. Assumptions • In females with G6PD deficiency, the over-presented allele is the mutant • X-inactivation pattern in leucocytes parallel that of erythroid cells

  41. Point of note • Absence of Class I mutants • Implies no acquired skewing due to somatic cell selection, typically seen in dyskeratosis congenita

  42. HUMARA study: results • Lyonization becomes increasingly skewed with age • 77.9% (62-97%) skewing in 9 elderly subjects • 60.4% (52-95%) skewing in offsprings • 62.3% (51-76%) in 20 young female controls

  43. Effect of lyonization on G6PD level • In female heterozygote carriers, the G6PD level correlated with age • G6PD level showed close correlation with that predicted from degree of lyonization • Expected G6PD activity = % normal allele x 0.38 IU/gHb + % mutant allel x 9.8 IU/gHb

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