Since the PAH gene is biallelic, and there are many disease causing mutations, most PKU patients are compound heterozygotes. (paper)

Compound heterozygosity in medical genetics is the condition of having two heterogeneous recessive alleles at a particular locus that can cause genetic disease in a heterozygous state. (wikipedia)

More than 400 disease-causing mutations have been found in the PAH gene. (wikipedia)

Why is Phenylalanine hydroxylase gene considered biallelic when PKU is also caused by the presence of two different mutant reccesive alleles at a locus with more that 400 types of mutations occurring in nature?

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    $\begingroup$ I've edited the link. $\endgroup$ – Tyto alba Feb 17 '17 at 8:44
  • $\begingroup$ In this context I would guess the "biallelic" was just meant to indicate that the gene is on a somatic chromosome (not X or Y), so that there is always two alleles of PAH in an individual. $\endgroup$ – Roland Feb 18 '17 at 13:13
  • $\begingroup$ @Roland Not only in this context but in many books(Principle of Genetics by Snustard for e.g) PKU is considered an autosomal recessive trait controlled by biallelic gene. Many times in other books too PKU has been mentioned in Pedigree analysis and Hardy Weinberg sums (taking only p and q the involved frequencies). $\endgroup$ – Tyto alba Feb 18 '17 at 13:24

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