A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait.

Verified step by step guidance

1. Step 1: Explain the inheritance pattern of Smith–Lemli–Opitz syndrome, which is an autosomal recessive disorder. This means that both parents must be carriers of the recessive allele for the child to be affected.
2. Step 2: Define what it means to be a carrier. A carrier has one normal allele and one mutated allele but does not exhibit symptoms of the disorder.
3. Step 3: Use a Punnett square to illustrate the genetic cross between two carrier parents. Each parent has a 50% chance of passing on the normal allele and a 50% chance of passing on the mutated allele.
4. Step 4: Calculate the probability of the offspring being affected. For each child, there is a 25% chance (1 in 4) of inheriting two mutated alleles, resulting in the disorder.
5. Step 5: Determine the probability of having two affected children. Since each child's genotype is an independent event, multiply the probabilities of each child being affected (0.25 * 0.25) to find the probability of both children being affected.

Key Concepts

Recessive Inheritance

Recessive inheritance refers to a pattern of genetic transmission where two copies of a mutated gene (one from each parent) are necessary for an individual to express a particular trait or disorder. In the case of Smith–Lemli–Opitz syndrome, which is inherited as a recessive trait, both parents must be carriers of the mutated gene for their child to be affected. If both parents are carriers, there is a 25% chance with each pregnancy that their child will inherit the disorder.

Carrier Status

Carrier status indicates that an individual possesses one copy of a mutated gene but does not exhibit symptoms of the associated disorder. In the context of Smith–Lemli–Opitz syndrome, both parents may be asymptomatic carriers, meaning they can pass the mutated gene to their offspring without being affected themselves. Understanding carrier status is crucial for genetic counseling, as it helps assess the risk of having affected children.

Genetic Counseling

Genetic counseling is a process that provides individuals and families with information about genetic conditions, including risks, inheritance patterns, and implications for future pregnancies. In this case, a genetic counselor would explain the likelihood of the parents having another child with Smith–Lemli–Opitz syndrome, emphasizing the 25% recurrence risk due to the recessive nature of the disorder. This counseling helps families make informed decisions regarding family planning and understanding their genetic health.