Transcript Vit B 12

Definition
Megaloblastic anemias are disorders caused by
impaired DNA synthesis due to the substances of
DNA synthesis deficiency, such as folic acid and
Vit B12,etc. It is characterized by the presence of
megaloblastic cells in the bone marrow and
macrocytic anemia.
Classification of MA
1.Vitamin B12 deficiency
2.Folate deficiency
3.Penicious anemia
The important role of folate and Vitamin B12
playing in the pathways of deoxynucleotide and
DNA synthesis:
Ribonucleotide
thymidylate synthetase
(N5,N10-methylene FH4)
dUMP
dTMP
dTTP
reductase
pyrimidine
synthesis
purine
synthesis
UTP(UR PPP ) → dUTP(UdRPPP)
CTP(CR PPP) → dCTP(CdR PPP)
ATP(AR PPP ) → dATP(AdR PPP)
GTP(GR PPP) → dGTP(GdR PPP)
D NA
1. De novo synthesis of purine:
N10-formyl FH4
C
7
N
1
N
FH4
C
C
2
C
C
N
N
8
2 . Thymidylate synthesis
thymidylate synthetase
d TMP
d UMP
N5,N10-methylene FH4
FH2
Glycine
Serine
FH2 reductase
FH4
3. Methionion synthesis
ATP
FH4
methionine
PPi+Pi
N5-methyl FH4 methyltransferase
(Vit B12)
N5-methyl FH4
Trap
S-adenosyl methionine
homocysteine
RH
adenosyl
R-CH3
H2O
S-adenosyl homocysteine
合成异常
DNA
dUTP
dTMP
dUMP
亚甲基四氢叶酸
巨幼变细胞
dTTP
二氢叶酸
DNA正常合成
叶酸缺乏
二氢叶酸还原酶
Vit B12 缺乏
四氢叶酸
甲硫蛋氨酸
高半胱氨酸
5-甲基四氢叶酸
叶酸和Vit B12缺乏对DNA合成的影响
Diet
Methyltetrahydrofolate
CH3
VitaminB12
Methionine
methylB12
Homocysteine
Tetrahydrofolate
purine and
pyrimidine
synthesis
Serine
Dihydrofolate
B6
glycine
Thymidylate
Deoxyuridylate
N5,N10-methylene FH4
DNA
Megaloblastic Anemias
Ineffective
erythropoiesis
Morphologically and functionally change
Megaloblastic cells
Defective DNA synthesis
Deficiency of folate and
Vit B12,etc.
Non-deficiency
Different disorders
Pathogenesis of MgA
Etiology of MgA
Food folate (daily needs 200μg)
Folate stores (5-20mg)
多聚谷氨酸叶酸
TFH- 多谷氨酸盐
liver
Enterohepatic
cycle
Excretion
blood
γ-谷氨酰胺羧基肽酶
FBP
urine
叶酸结合蛋白
单谷氨酸叶酸
甲基//四氢叶酸
+Vit B12
蛋氨酸循环
叶酸的吸收、利用、贮存和排泄
DNA 合成
tissue
绿叶蔬菜、柠檬、香蕉、瓜
类、香菇、酵母及动物内脏
（尤其是肝脏）等都含大量
叶酸。
1.The causes of folic acid deficiency
I inadequate intake(diet)
II intestinal malabsorption
III increased demand
IV inability to utilize folate due to action of
folate antagonists
Food Vit B12 (daily needs 2 ～ 5μg)
Vit B12 stores
liver
IF
(4 ～5mg)
Enterohepatic
cycle
Vit B12 –IF
blood
TcII-B12
Vit B12
+ 甲基叶酸
释放内因子
Excretion
urine
faeces
tear
saliva
milk
蛋氨酸循环
tissue
Vit B12的吸收、利用、贮存和排泄
动物的肝、肾、
肉类、禽蛋、
乳类和海洋生
物等B12含量较
多。
2. The causes of Vitamin B12 deficiency
I. inadequate intake
II. intestinal malabsorption
III. vitamin B12 destruction
IV. congenital defects
Clinical Features LaboratoryFeatures
Clinical Features
1. Common manifestations
• Anemia develops slowly, severe anemia with
weakness, palpitation, fatigue, light-headedness,
and shortness of breath.
• Slight jaundice
• Glossitis
2. Different features caused by different disorders
Vit B12 deficiency:
•peripheral neuropathy and subacute combined
degeneration of the spinal cord with nervous system
symptoms such as numbness and tingling of the
extremities, loss of position sense, muscle weakness
and decreased tendon reflexes.
Folate deficiency :
not produce nervous system manifestations.
Pernicious anemia
• abdominal pain, diarrhea, nausea, and vomiting
• nervous system symptoms.
ATP+VitB12
腺苷钴胺
adenosylcobalamin
Methylmalonyl CoA
Succinyl CoA
甲基丙二酰辅酶A
琥珀酰辅酶A
代谢产物堆积，血、尿可测
合成神经鞘磷脂
Laboratory Features
Blood
•macrocytic anemia, with MCV↑(100~150fl or more).
•But coexisting IDA, Thalassemia trait, or inflammation
may prevent macrocytosis.
•Erythrocytes show marked anisocytosis and
poikilocytosis, with many oval macrocytes and in severe
cases, basophilic stippling, Howell-Jolly bodies, and
Cabot rings
•Megaloblastic normoblasts may be seen.
•Ret count is low.
•Leukopenia and thrombocytopenia are frequently
present.
•“Hypersegmented neutrophils” (more than five
lobes) are an early sign of megaloblastosis.
--Platelets:smaller and vary more widely in
size.(PDW increase)
Bone Marrow:
--Moderate or marked hypercellularity.
-- M/E ratio ↓
--Erythroid hyperplasia with striking megaloblasts
(more than 10%). Promegaloblasts and early
megalonormoblasts increase with mitotic figures
abundant in severe cases.
•basophilic stippling, Howell-Jolly bodies, and
Cabot rings may be seen.
The characteristics of megaloblasts:
1. Cells and nuclei are larger in size
and the chromatin is more looser.
2. Marked nuclear-cytoplasmic
asynchrony.
The development of the nucleus is
behind that of cytoplasm, called
“young nucleus and old cytoplasm”
Pathogenesis of MgA
Impaired synthesis of one or more deoxyribonucleotides
DNA replication and cell division are blocked,while
synthesis of cytoplasm(RNA and protein) proceeds
normally.
RNA/DNA ratio rises
and cytoplasm is
basophilic
Chramatin is looser
Cells are larger in size
megalopronormoblast
pronormoblast
Polychromatic
megalonormoblast
Early normablast
Normoblasts and
megalonormoblast
Orthochromatic normoblast
Megaloblastic changes
核畸形、多核、核
碎裂的巨幼红细胞
Howell-Jolley bodies
Basophilic stippling
normoblast
Myeloid megaloblastic changes
The megaloblastic myeloid cells may be
larger in size, deforming nucleus with looser
chromatin; specific granules reduce and
vacuoles appear in cytoplasm. Hpersegmented
neutrophils (also be seen in the peripheral
blood) and giant metamyelocytes and bands
present.
Megakaryocytic megaloblastic changes
Megakaryocytes are usually present
either in normal or slightly increased
numbers, but occasionally they are
decreased in number, some are atypical
and have a deeply basophilic agranular
cytoplasm or hypersegmented nucleus.
Tests for determining the causes of MA
--Serum vitB12 (RIA <74~103 pmol/L)
--Urinary excretion of methylmalonic acid
--Serum folate assay( <6.91nmol/L or <3 ng /ml)
--The red cell folate assay (RIA)< 227 nmol/L
--Folic acid therapy test
--Intrinsic factor and its antibody
【Diagnosis】 Two steps:
1.To establish the anemia is of MA
2.To determine the cause of the anemia.
Diagnosis of typical MA:
--Macrocytic—normochromic anemia
--Megaloblastic haemopoiesis of erythroid.
--Myeloid and megakaryocytic series are
involved also.
When MA is atypical, how to diagnose it?
Clinical features: history, signs, and
specific tests
Myeloid megaloblastic changes
Why myeloid megaloblastic changes take an
important role
--Minimal anemia or no anemia, erythroid changes
have not appeared when the myeloid megaloblastic
changes present.
--Dimorphic anemia(MA +IDA), the blood will
show a small number of oval macrocytes and almost
always neutrophil hypersegmentation ; the marrow
usually show intermmidiate megaloblasts and giant
stab forms.
--After treatment, the myeloid changes still
present when erythroid megaloblasts
disappear.
--If MgA with hypocellularity when
pregnancy, megaloblastic normoblasts and
megakaryocytes are seldom seen,
megaloblastic changes in myeloid are
distinctive.
Questions:
1. What are the characteristics of
megaloblastic cells?
2. Why myeloid megaloblastic changes
sometimes take an important role in the
diagnosis of MA?
3. What are the common cause of MA?
4. How to diagnose MA caused by folic acid
deficiency, Vit B12 deficiency,or pernicious
anemia?
ANEMIA
贫
红细胞生成减少
骨髓造血
功能障碍
干细
胞增
殖分
化障
碍
再
障
，
纯
红
再
障
等
骨
髓
增
生
异
常
综
合
征
等
骨髓
被异
常组
织侵
害
白 骨
血 髓
病、纤
骨 维
髓 化
瘤、等
癌
转
移、
红细胞破坏过多
造血物质缺乏
或利用障碍
骨髓
造血
功能
低下
肾 内
病、分
肝 泌
病、疾
感 病
染 等
性
疾
病、
铁缺
乏和
铁利
用障
碍
缺铁
铁粒
性幼
贫细
血胞
性
贫
血
等
血
红细胞
内在缺陷
膜异常 酶异常
维生
素B12
阵 遗 遗 葡 丙
或叶
发 传 传 萄 酮
酸缺
性 性 性 糖 酸
乏
睡 椭 球 6 激
眠 圆 形 磷 酶
巨
性 红 红 酸 缺
幼
血 细 细 脱 乏
细
红 胞 胞 氢 症
胞
蛋 增 增 酶 等
贫
白 多 多 缺
血
尿 症 症 乏
等
症 等
症
外在异常
红细胞丢
失增加
急
Hb异常 免疫 非免疫 性
失
因素 因素
血
珠 异 不
蛋 常 稳 各 微 化 脾 性
白 血 定 种 血 学、功 贫
生 红 血 原 管 物 能 血
成 蛋 红 因 病 理、亢
障 白 蛋 致 性 生 进
碍 病 白 免 溶 物
病 疫 血 因
性
贫
性 性 素
血
溶 贫 致
血 血 溶
血
性
贫
血
贫血的病因及发病机制分类
慢
性
失
血
性
贫
血
Anemia: weakness,fatigue, listlessness,palpitation, pallor jaundice,
splenomegaly
MCV
increase
MCH
MA
normal
decrease
IDA,SA,Thala
MCHC
infection
decrease
hypopoiesis
decrease
ret
PL
normal
infection
WBC
decrease
AA,MF
increase
acute loss blood
HA (Coomb’s)
IHA
extracellular defect
chronic renal disease
increase
AM
increase
intra-
osmotic fragility
normal
HS,HE, G-6PD, PK
decrease
Thala
PNH (ham’s) abnormalHb
Diagnostic steps of HA:
history,infection, underlying diseases,drugs,pallor,weakness
dark urine, jaundice,hepatosplenomegaly
blood film
spherocytes,
autoagglutination,
ret increased
cold agglutinin test
red cell fragments
immune assay
Coomb’s test
positive
CAS
AIHA
negative
cold warm
hemolysis test
transfusion reaction
infection, congenital syphilis
Normocytic normochromic anemia
history, underlying diseases, pallor,weakness
blood film
decrease/ increase
ret
morphologic features
normal
secondary
increase
acute blood loss
abnormal
hypoplasia
abnormal proliferation
anemia
Infection
renal disease
liver disease
endocrinic disease
HA
infiltration in marrow
AA
MDS
leukemia
MF
metastatic cancer
Microcytic hypochromic anemia:
history, underlying diseases, anemia,MCV,MCH
Blood film
SI
increased
Iron stain
normal/ increased
decreased
Hb eletrophoresis
SF
HbA2,F
increased
SA
normal/ increased decreased
Thalasemia
HbC,S, D,E
etc.
anemia of chronic
disorders
IDA
Differentiation of macrocytic anemias:MCV,MCH
history, anemia ,underlying diseases,
drugs,nutrition,neurologic signs, hepatosplenomegly
blood film
increased
normal / decreased
Ret
marrow morpholoy
acute blood loss HA
non-MA
MA
erythroblastic anemia abnormal proliferation
Alchohol poisoning
Liver disease
MDS
Folate deficiency
VitB12 deficiency
Pernicious anemia