X-Linked Recessive Disorder

Md. Tangigul HaqueReg. No. : 2011433023

• 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

• 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

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 ofCarrier Mother And Affected Father

• 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

• 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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