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Phenotypic diversity in siblings with partial androgen insensitivity syndrome
B A Evans1, I A Hughes, C L Bevan
1Department of Child Health, University of Wales College of Medicine, Heath Park, Cardiff.
Archives of Disease in Childhood
|June 1, 1997
Summary
Androgen insensitivity syndrome (AIS) is caused by androgen receptor gene mutations. A specific mutation, arginine 840 to cysteine, resulted in varied physical traits in siblings, indicating other factors influence AIS.
Area of Science:
- Genetics
- Endocrinology
- Molecular Biology
Background:
- Androgen insensitivity syndrome (AIS) presents a spectrum of disorders due to defective androgen receptor (AR) protein.
- AR gene mutations impair normal androgen action, leading to incomplete virilization.
Observation:
- A specific point mutation (arginine 840 to cysteine) in the AR gene was identified in two siblings with partial AIS.
- Phenotypic presentation varied significantly between siblings, despite the shared mutation.
Findings:
- One sibling exhibited cliteromegaly and labial fusion, raised female.
- The other sibling presented with micropenis and hypospadias, raised male.
Implications:
- Phenotypic variability in AIS is influenced by factors beyond AR gene mutations alone.
- Understanding these additional factors is crucial for accurate diagnosis and management of AIS.
- This case highlights the complex interplay of genetics and other biological elements in determining sex development.
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01:35Pedigree Analysis
Overview
01:33Pleiotropy
Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause Waardenburg Syndrome Type 4, or WS4, which can cause defects in pigmentation, hearing impairments, and an absence of intestinal contractions necessary for elimination. This diversity of phenotypes results from the expression pattern of SOX10 in early embryonic and fetal development. SOX10 is found in neural crest cells that form melanocytes,...
01:19X-linked Traits
In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
01:43Sex-linked Disorders
Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological deficits, the disorder is considered sex-linked.
01:43Incomplete Dominance
Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.
02:27Background and Environment Affect Phenotype
Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...
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