A male newborn presents with severe hypotonia and his mother shows little emotional expression. What genetic phenomenon most likely explains their conditions?

• A. Gonadal mosaicism
• B. Mitochondrial inheritance
• C. Uniparental disomy
• D. Expanded trinucleotide repeats

Answer: (D)

The condition presented in the scenario, characterized by severe hypotonia in the male newborn and little emotional expression in the mother, is most likely explained by expanded trinucleotide repeats, a genetic phenomenon commonly associated with certain hereditary disorders.

Expanded trinucleotide repeats involve a sequence of three nucleotides that are repeated multiple times in a gene. When the number of repeats exceeds a certain threshold, it can lead to neurological disorders. One relevant example is Fragile X syndrome, which is caused by the expansion of CGG repeats in the FMR1 gene. This condition can manifest as developmental delays, intellectual disability, and emotional expression issues, which may be reflected in the mother’s emotional demeanor.

The connection between the mother and child in this scenario suggests that a genetic disorder related to expanded trinucleotide repeats could manifest characteristics in both, such as the mother’s emotional flatness potentially indicating her own carrier status for a condition like Fragile X syndrome, while the severe hypotonia in the newborn may reflect the phenotypic effects of the expanded repeats in the child.

This phenomenon highlights the importance of genetic inheritance patterns, particularly when both maternal expression and offspring effects are considered. Understanding expanded trinucleotide repeats provides insights into both the inheritance and clinical implications seen here.