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: Begin by explaining that Smith–Lemli–Opitz syndrome is inherited as an autosomal recessive trait. This means that for a child to be affected, they must inherit two copies of the defective allele (one from each parent). Each parent must therefore be a carrier of the recessive allele (heterozygous).
2. Step 2: Use a Punnett square to model the inheritance pattern. Assign 'A' to represent the normal allele and 'a' to represent the recessive allele causing the syndrome. Cross two heterozygous parents (Aa x Aa) to determine the probabilities of their offspring's genotypes.
3. Step 3: From the Punnett square, determine the genotypic ratio of the offspring: 1 AA (homozygous dominant, unaffected), 2 Aa (heterozygous carriers, unaffected), and 1 aa (homozygous recessive, affected). This results in a 25% chance of an affected child (aa), a 50% chance of a carrier child (Aa), and a 25% chance of an unaffected non-carrier child (AA).
4. Step 4: To calculate the probability of having two affected offspring, multiply the probability of having one affected child (25% or 0.25) by itself, since the events are independent. This gives the probability of both children being affected.
5. Step 5: Conclude by explaining that the recurrence of the syndrome in the second child is consistent with the autosomal recessive inheritance pattern. Emphasize the importance of genetic counseling for the parents to understand their carrier status and the associated risks for future pregnancies.

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 for a recessive disorder but does not exhibit symptoms of the disorder themselves. In the context of the case, both parents may be asymptomatic carriers of the Smith–Lemli–Opitz syndrome gene mutation. Understanding carrier status is crucial for genetic counseling, as it helps assess the risk of having affected offspring in future pregnancies.

Genetic Counseling

Genetic counseling is a process that provides individuals and families with information about genetic conditions, including risks, inheritance patterns, and implications for health. In this case, a genetic counselor would explain the likelihood of the parents having another child with Smith–Lemli–Opitz syndrome, emphasizing the importance of understanding their carrier status and the probabilities associated with recessive inheritance. This guidance is essential for informed family planning.