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552 PART 7 ■ Principles and Disorders of Hemostasis and Thrombosis

X-linked reces s ive gene inheritance

Example: Hemophilia A (classic hemophilia)

Father: healthy Mother: healthy carrier

Genetically and ,

clinically normal hemophilia A trait

asymptomatic Maternal chromosome Maternal chromosome

carrier

Abnormal X Normal X

Normal Normal Abnormal Normal

X Y X X Defective gene for Normal gene for

coagulation factor VIII coagulation factor VIII

Paternal chromosome Child A Child B

Normal X

Normal gene for Female (XX) Female (XX)
coagulation factor VIII Healthy, carrier Healthy, normal
chromosomes

Paternal chromosome Child C Child D

Normal Y

No genetic influence Male (XY) Male (XY)

on X chromosome Hemophilia Healthy, normal
chromosomes

FIGURE 28.1 X- inke recessive gene inheritance. Exa e: C assic he o hi ia (he o hi ia A). T e e ective

gene on the X chro oso e is ex resse in a es on y because the Y chro oso e contains no atching nor a

gene (a e e) to o set the e ect o the e ective X gene. (Fro McConne H. Te Nature o Disease Pathology or
the Health Pro essions, Phi a e hia, PA: Li incott Wi ia s & Wi kins, 2007.)

P as a eve s o actor VIII can be te orari y correcte Etiology

an the b ee ing ten ency reverse in ost atients o ow- He o hi ia invo ves a artia or co ete e ciency o the

ing in usion o actor VIII in a ro riate b oo ro ucts. actor IX. Most atients e cient in actor IX have oint

One wou ex ect that correction o the he ostatic e ect utations; the nature o the utation eter ines the eve

wou ace a atient at the sa e risk o thro boe bo is o actor IX activity. More than one thir o the utations

as an una ecte in ivi ua , but thro boe bo ic events in a ect critica arginine resi ues resu ting in a ys unctiona

atients with he o hi ia A are istinct y unco on. o ecu e.

Laboratory Findings Epidemiology

Laboratory assay revea s a ro onge activate artia thro - He o hi ia B is ess co on than he o hi ia A. T is ac-

bo astin ti e (AP ), nor a rothro bin ti e (P ), an tor e ciency is sex inke an occurs at a rate o 1/30,000

a nor a thro bin ti e ( ). A actor assay is necessary or o a e births with a e ective o ecu e being the usua

e nitive iagnosis ( ab e 28.1). cause.

Hem ophilia B Signs and Symptoms

Factor IX e ciency is known as hemophilia B or Christmas He o hi ia B is c inica y in istinguishab e ro he o-

disease. hi ia A an ust be i erentiate by aboratory testing. T e