Recessive gene, definition

Infants with salt-losing crisis and adrenal insufficiency in infancy may have adrenal hypoplasia congenita. This can be of two types recessive, for which the cause has not been defined and which affects mostly the fetal zone, and X-linked, which is caused by mutations in the DAX-1 gene, which (with steroidogenic factor-1) controls definitive zone development and steroidogenesis [71]. GC-MS analysis of patients with the disorder show variant patterns from absence of neonatal A5 steroids, appropriate for the recessive form [81], to extremely low cortisol production and transient 11/Lhy-droxylase deficiency, as evidenced through increased THS excretion (Malunowicz, personal communication). 

The first definitive studies were performed in Britain during World War II by Charlotte Auerbach.19 After the observation that injuries from war gases resembled x-ray burns, Auerbach demonstrated unequivocally that mustard gas induced sex-linked recessive lethal mutations in Drosophila. At about the same time, I. A. Rapoport361 independently reported that several other chemicals induced gene mutations and chromosomal aberrations. Their work ushered in the era of chemical studies of mutation, and within a few years a large number of chemical mutagens had been identified. 

The incidence of phenylketonuria is about 1 in 20,000 newborns. The disease is inherited in an autosomal recessive manner. Heterozygotes, who make up about 1.5% of a typical population, appear normal. Carriers of the phenylketonuria gene have a reduced level of phenylalanine hydroxylase, as indicated by an increased level of phenylalanine in the blood. However, this criterion is not absolute, because the blood levels of phenylalanine in carriers and normal people overlap to some extent. The measurement of the kinetics of the disappearance of intravenously administered phenylalanine is a more definitive test for the carrier state. It should be noted that a high blood level of phenylalanine in a pregnant woman can result in abnormal development of the fetus. This is a striking example of maternal-fetal relationships at the molecular level. Table 23.3 lists some other diseases of amino acid metabolism. 

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