This document discusses X-linked recessive disorders. Key points include: - X-linked recessive disorders are passed down through families on the X chromosome. - Males are usually affected because they only have one X chromosome, so only one abnormal gene is needed to cause the disease. - Females can be carriers and pass the abnormal gene to their sons but usually do not show symptoms themselves because they have a second normal X chromosome.

1. X-Linked Recessive Disorder
Md. Tangigul Haque
Reg. No. : 2011433023

2. • Passed down through families through one of the X chromosomes
• If only one gene in the pair is abnormal, the disease does not occur
or it is mild
• Someone who has one abnormal gene is called a carrier
• Carriers can pass abnormal genes to their children
• The term X-linked recessive usually refers to “Sex-linked
recessive”.1
Reference:1. Fogel BL, Geschwind DH. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC.Fogel BL, Geschwind DH. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC.
Bradley's Neurology in Clinical Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 40.
X-Linked Inheritance

3. • Males affected almost
exclusively
• A single recessive gene on
that X chromosome will
cause the disease.
• The gene alteration can be
transmitted from female
carriers to sons
• Affected males cannot
transmit the condition to their
sons.
Fig: X-linked recessive inheritance condition
Reference: Dobyns, William B.; Filauro, Allison; Tomson, Brett N.; Chan, April S.; Ho, Allen W.; Ting,
Nicholas T.; Oosterwijk, Jan C.; Ober, Carole (2004). "Inheritance of most X-linked recessive traits” .
American Journal of Medical Genetics 129A (2): 136.
Features of X-Linked Recessive Inheritance

4. Fig: X-linked recessive, carrier mother Fig: X-linked recessive, affected father
Reference: Wattendorf DJ, Hadley DW Am Fam Physician, Family history: the three-
generation pedigree. 2005 Aug 1; 72(3):441-8.[PubMed]
Reference: Wattendorf DJ, Hadley DW Am Fam Physician, Family history: the three-
generation pedigree. 2005 Aug 1; 72(3):441-8.[PubMed]
X-Linked Recessive – In Case of
Carrier Mother And Affected Father

5. • Most types are caused by a gene
located on the X chromosome
• Red green colorblindness is the
most common type
Fig: Ishihara Test
Reference: Troscianko T, Benton CP, Lovell PG, Tolhurst DJ, Pizlo ZPhilos Trans R Soc
Lond B Biol Sci. on visual perception. 2009 Feb 27; 364(1516):449-61.[PubMed]
Example 1 - Colorblindness

6. • Much rare than colorblindness
-1 in 10,000 males
-1 in 100,000,000 females
• Hemophilia A is a disorder where the blood cannot clot
properly due to a deficiency of a clotting factor called
Factor VIII. This results in abnormally heavy bleeding
that will not stop, even from a small cut. 2
Reference: 2. Sankiewicz P, Lupsik JR. Gene, genomic, and chromosomal disorders. In: Goldman L, Ausiello D, eds.Sankiewicz P, Lupsik JR. Gene,
genomic, and chromosomal disorders. In: Goldman L, Ausiello D, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders;
2011:chap 40.
Example 2 - Hemophilia

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