Suggest how DD1 causes ${\beta }_2$-microglobulinuria.

DD1 results from a sex-linked recessive mutation in the CLCN5 gene. In a male with DD1, where would this mutation be located? Select (✓) one box.

[ ] The homologous section of a Y chromosome

[ ] The homologous section of an X chromosome

[ ] The non-homologous section of a Y chromosome

[ ] The non-homologous section of an X chromosome

Scientists investigated the use of transplanted stem cells to treat DD1 in mice. They set up four experimental groups:

• Group W – 60 wild-type mice (not affected by DD1)
• Group X – 60 mice with DD1
• Group Y – 60 mice with DD1 that received stem cells from mice with DD1
• Group Z – 60 mice with DD1 that received stem cells from wild-type mice

After 16 weeks, the scientists measured the concentration of ${\beta }_2$-microglobulin in the urine using a scale from 0 (undetectable) to ++++ (highest concentration). The results are shown in Table 1.

Table 1

Using all the information provided, evaluate the use of stem cells to treat DD1 in humans.

The scientists carried out further work to investigate how the transplanted stem cells developed after transplantation.

• They transplanted stem cells from wild-type male mice into adult female mice with DD1.
• After 16 weeks, they found that ${\beta }_2$-microglobulinuria in these female mice had significantly decreased.
• On examining proximal tubule tissue from the female mice, they found that some of these cells contained a Y chromosome.

Suggest how the transplanted stem cells reduced ${\beta }_2$-microglobulinuria.