X-LINKED RECESSIVE CONDITIONS
In X-linked recessive conditions, males with a mutant recessive gene on the X chro-mosome have the condition, while daughters of affected males are obligate carriers, who in many situations are asymptomatic.
· Sons of affected males do not carry the mutation.
· Daughters of carrier females may be either normal or carriers.
· Sons of carrier females may be affected or normal (because males are hemi-zygous for the X chromosome).
Lesch-Nyhan syndrome results from deficiency of hypoxanthine-guanine phophori-bosyltransferase (HGPRT), which impairs salvaging of the purines hypoxanthine and guanine. Clinical features include intellectual disability, hyperuricemia, and self-mutilation.
Testicular feminization is an androgen insensitivity that causes failure of normalmasculinization of external genitalia of XY males.
In Bruton agammaglobulinemia, defective Bruton tyrosine kinase (Btk) at band Xq21.3 causes complete failure of immunoglobulin production characterized clini-cally by complete absence of antibodies in serum and recurrent bacterial infections.
In Menkes disease, a mutation of the ATP7A gene impairs copper distribution.
Infants show failure to thrive, and death occurs in the first decade.
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