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STUDIES
Year : 1992  |  Volume : 58  |  Issue : 3  |  Page : 179-182

Mode of inheritance in psoriasis




Correspondence Address:
Arvind Kumar


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  Abstract 

One hundred and eighty patients of psoriasis and 100 controls were analysed to find out the genetic nature of psoriasis and if so, then to determine the possible mode of inheritance. The prevalence of psoriasis in relatives, percentage of positive family history and percentage of total affected relatives in the patient group was significantly higher than the controls, and clustering of affected relatives in patient group suggested genetic involvement. Ratio of affected and unaffected in the sibships with unaffected parents and one parent affected and ratio in the children of patients suggested polygenic mode of inheritance.


Keywords: Psoriasis, Inheritance, Polygenic


How to cite this article:
Kumar A, Mohan L, Singh K K, Pandey O N, Mu. Mode of inheritance in psoriasis. Indian J Dermatol Venereol Leprol 1992;58:179-82

How to cite this URL:
Kumar A, Mohan L, Singh K K, Pandey O N, Mu. Mode of inheritance in psoriasis. Indian J Dermatol Venereol Leprol [serial online] 1992 [cited 2020 Feb 21];58:179-82. Available from: http://www.ijdvl.com/text.asp?1992/58/3/179/3789



  Introduction Top


The familial pattern of psoriasis has been reported by many workers. Hoede (1931) concluded that psoriasis is inherited by an autosomal dominant gene. Steinberg et al (1951) suggested that double recessive genes may be responsible. Balyavichene (1969) [3] suggested that psoriasis is a multifactorial disorder. Farber (1971) [4] recorded psoriasis in 10.6 percent of brothers, sisters and children, 4.2 percent of their uncles, aunts, grandparents, and 1.4 percent of their cousins, while only 2.6 percent, 0.4 percent and 0.9 percent respectively of control relatives had psoriasis. Watson et at (1972) [5] analysed the incidence of psoriasis in siblings where the index case had neither parent with psoriasis, one parent with psoriasis or both parent with psoriasis. For the first the value was 7.5 percent, for second 15 percent and for third 50 percent. He proposed psoriasis to be a multifactorial disorder. Mori et al (1980) [6] have also stressed on the genetic factor in the development of psoriasis in their study on monozygotic twins. Nigam and Mukhija (1985) [7] reported psoriasis in monozygotic twins, where possible mode of inheritance was autosomal recessive.


  Materials and Method Top


One hundred and eighty patients (5 to 73 years, male to female ratio 1.8:1) and 100 age and sex matched controls were studied between November 1990 and December 1991. Detailed family history was taken in 3 to 4 generations in first, second and third degree relatives with presence of psoriasis in their sibs, sib's children, parents and their sibs and children, grandparents and their sibs and distant relatives.


  Results Top


The affected relatives showed clear preponderance in the psoriasis group than in the controls. Prevalence of psoriasis in relatives was 0.4228 percent in the patient group and 0.075 percent in the controls [Table - 1].

There was clustering of affected relatives in psoriasis patients [Table - 2]. Percentage of familial affection was more (15.00 percent) in the patient group than in the control group (2.00 percent), and percentage of total affected relatives was 17.77 percent in patient group and 3.00 percent in the controls [Table - 2],

Patients with no parent affected had 1:3.26 (184:600) ratio of affected and unaffected in the sibship and with one parent affected had a ratio of 1:2,555 (9:23).

The ratio of affected and unaffected children of the patients was 1:147 (3:441),


  Comments Top


Comparative evaluation of the relatives revealed clear preponderance of psoriasis in the patient group than in the controls, The prevalence of psoriasis in the relatives of the patients was more as compared to the controls and the difference was highly significant (p < 0.01, x 2=10.5112 at 1 d,f,, z=3.236). Twenty seven patients (15.00 percent) had positive family history, while only 2 controls (2.00 percent) had positive family history, the difference was highly significant (p < 0.01, x 2=11.72 at 1 d.f,, z=3,43). Total affected relatives of patients were 32 (17.77 percent) and of controls were 3 (3.00 percent), the difference was also highly significant (p < 0,01, x ,2 =10.41 at 1 d.f., z=3.60).

With no parent affected, the ratio of affected and unaffected in the sibship was 1:3.26. In autosomal recessive disease, ratio in the sibship should be 1:3, if both parents were heterozygous. With one parent affected, the ratio was 1:2.555. For the disease to be autosomal dominant the ratio should be 1:1, if one parent is affected. The data suggest that psoriasis is a multifactorial disorder.

The ratio of affected and unaffected children of patients was 1:147. In autosomal dominant inheritance, the children should be affected in 1:1 proportion but the data contradicted this. In autosomal recessive disease, when one affected case marries a phenotypically normal partner, the chances of normal partner being heterozygous for psoriasis would be 1 in 19 [If we consider psoriasis to be an autosomal recessive disease and 0.075 percent prevalence of psoriasis among relatives of controls representing in general population, then calculation by Hardy-Weinberg's Law (p2+p 2+2pq=1, if p is normal gene frequency and q is psoriatic gene frequency and 1 is general population), the heterozygous- in general population would be 5.3 percent and there would be 1 heterozygous in 19 normal persons in outward appearance. Thus, if 19 psoriasis patients marry 19 partner normal in outward appearance, 1 partner would be heterozygous and children of those 19 couples will show ratio 1:37). However, data shows affected and unaffected ratio to be 1:147 excluding autosomal recessive inheritance, and strongly suggest the polygenic inheritance of psoriasis.

 
  References Top

1.Hoede K. Umwelt and Erblichkeit bei der Entstehung der schuppenflechte. Wurzburger Abhandlunge Ges Med 1931; 27:211.  Back to cited text no. 1    
2.Steinberg AG, Becker SW, Fitzpatrick TB. A genetic and statistical study of psoriasis. Am J Hum Genet 1951, 3:267-81. - - -  Back to cited text no. 2    
3.Balyavichene GR. Psoriasis and hereditary Vest Dermatol Venereol 1967, 43:31-5.  Back to cited text no. 3    
4.Farber EM. Epidemiology and genetics of psoriasis. Jap J Dermatol 1971, 81:632-9.  Back to cited text no. 4    
5.Watson W, Cann HM, Farber EM, et al. The genetics of psoriasis. Arch Dermatol 1972 105:97.  Back to cited text no. 5  [PUBMED]  
6.Mori N, Yoshikawa K, Ohno M. Psoriasis occuring in young monozygotic twins. J Dermatol (Tokyo) 1980, 7:71-3.  Back to cited text no. 6  [PUBMED]  
7.Nigam P, Mukhija RD. Psoriasis in Monozygotic twins. Ind J Dermatol Venereol Leprol 1985, 51:236-7.  Back to cited text no. 7    


    Tables

[Table - 1], [Table - 2]



 

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