Many of the genes known in man are pleiotropic in their effects, with , in some cases,considerable variability in the manifestation of each of the different effects of the gene.Thus,in marfan’s disease(arachnodactyly) it is very probable that a single dominant factor determines congenital subluxation of thelens,a characteristic elongate body build,congenitalheart disease,etc.

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GOUT:

Gout is a disorder of uric acid metabloism characterized chiefly by hyperuricemia; acute and recurring attacks of painful arthiritis; tophaceous deposits of sodium urate crystals in articular,   periarticular, subcutaneous tissues; and in the later stages,vascular lesions, and renal lesions with nephrolithiasis.Atleast 90% affected persons are males.

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EPILEPSY:

Epilepsy is a chronic disorder characterized by sudden loss of consciousness, which may be only momentary, or which may be prolonged and accompanied bya convulsion.There exist many variants of the disease.Recently, consierable attention ahas been directed towards the so-called epileptic equivalents, these consisting of mental states characterised by amnesia, automatism, periods of excitement, etc.

Pheylpyruvic amentia(phemylketoniria) is arare charcteised by amnmetia.The exact relation between the metabloic  abnormality as revealed by studies of the urine and the mental condition is not known. 

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THALASSEMIA:

Thalassemia(cooley’s anemia) is a chronic,fatal,progressive anemia of childhood characterized by a hypochromic,microcytic anemia,peripheral erythroblastosis,ssplenomegaly, a characteristic mongoloid facies,hyperplasia of the bone marrow resulting in typical x-ray findings, and a familial incidence.Moncrieff and whitby suggested that the disease was due to a single recessive factor.The disease was first described by cooley and lee in 1925.

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SICKLE CELL ANEMIA:

Sickle cell anemia is a chronic anemia confined confined almost entirely to negroes and chracterised clinically by rheumatoid pains,leg ulcers,hemolytic crises,hyperplasia of the bone marrow with typical x-ray findings,the general symptoms of anemia and a chracteristic hematologic picture. The finding from which the disease derives its name iss the occurrence of elongate ,pointed,often,often curved,”sickle” shaped erythrocytes in thr peripheral blood. These may be observed in small numbers on stained smears of fresh peripheral blood.

Pernicious anemia is a chronic disorder usually developing insidiously in late adult life and characterised bya progressive,severe macrocytic anemia accompanied by the usual symptoms of a profound anemia; evidence of increased blood destruction;achlorhydria; and neurological and gastrointestinal symptoms.

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FIBRINOGEN:

A fibrinogen is a very rare disease characterised by the absence of blood fibrinogen, with incoagulability of the blood and a consequent tendency to fatal hemorrhage. Primary fibrinogenopenia is a similar but less extreme condition, characterized by a marked decrease in fibrinogen. The frequency of the latter disease is unknown, since even in the face of a markedly reduced fibrinogen the coagulation of the blood tends to remain normal,and only the most extreme reductions are detected normally.