Mr. and Mrs. Sanchez recently had a baby girl (Susie) and she has been diagnosed

Question

Mr. and Mrs. Sanchez recently had a baby girl (Susie) and she has been diagnosed with PNDM. Since treatment for PNDM varies depending on what the cause is, the pediatrician ordered DNA sequencing to look for mutations in genes associated with this disorder. Below are the DNA sequencing results that her pediatrician ordered.

Patient Name: Susan Sanchez

Age: 8 months

KCNJ11 gene:

1 Change found in ONE copy of chromosome 11

Nucleotide 157 G to A

This change corresponds to the first nucleotide in the 53rd codon.

Wild-type codon reads GGC

INS gene:

1 Change found in ONE copy of chromosome 11

Nucleotide 218 A to G

This change corresponds to the third nucleotide in the 72nd codon.

Wild-type codon reads CGA

Based on the results above, what mutation do you predict is contributing to Susie?s phenotype?

Question 2: Data from the NCBI Gene Review database suggests that the mode of inheritance of PNDM is autosomal dominant for mutations in KCNJ11 and autosomal recessive for mutations in ABCC8 and INS. Based on this information and your answers to the question above, which of the following two pedigrees representing PNDM likely represents Susie and her family (Circle one). Justify your answer using 3 sentences or less.

Explanation / Answer

Answer 1-

Since there is change in just one nucleotide, like one purine to another – A to G or G to A. This kind of mutation is SUBSTITUTION. Here due to change in one nucleotide, the codon reads another amino acid than the wild type, leading to disruption in function of respective protein and occurrence of disease.

Answer 2-

It can be the 2nd pedigree. Considering 8 & 9 as Mr. & Mrs Sanchez and 17 as Susie. From father’s side, since the disease is shown in every generation, means PNDM responsible (both recessive and dominant mutant genes are there). From the mother’s side, its not repeating after every generation, but chances of being a carrier for the recessive gene is there. So we can assume it’s the family pedigree.

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