The relationships match what was declared. Elena and Marc both carry cystic fibrosis, so each pregnancy has a 1 in 4 chance of an affected child. Lía inherited Elena's copy only: she is a carrier, not affected. Her FMR1 repeat grew from 48 to 49, still intermediate, and her RhD-negative blood came from both parents. One new change in Lía passed the filters, outside any gene.
Every declared parent and child shares about half their DNA, and Elena and Marc are unrelated. No sample was swapped.
| Pair | Shared | Stretches | Longest | Reads as | Check |
|---|---|---|---|---|---|
| Elena · Lía | 3,389 cM | 23 | 281.4 cM | parent and child | agrees |
| Marc · Lía | 3,381 cM | 25 | 267.9 cM | parent and child | agrees |
| Elena · Marc | 5.1 cM | 2 | 2.9 cM | unrelated, or beyond 4th degree | agrees |
They share one gene: CFTR, cystic fibrosis. Elena carries p.Phe508del and Marc p.Gly542Ter, both pathogenic with three review stars. Neither is affected. Each pregnancy is a fresh draw of four equally likely children:
What to do: before another pregnancy, a genetic counsellor can explain the options: clinical carrier confirmation, and prenatal or preimplantation testing.
| Condition | Marc | Elena | For a child |
|---|---|---|---|
| Cystic fibrosis CFTR | carrier | carrier | 1 in 4 affected |
| Phenylketonuria PAH | carrier | none found | may be a carrier; not affected unless Elena carries a change the screen misses |
| Haemochromatosis HFE | none found | carrier | may be a carrier |
| Fragile X FMR1 | 30 repeats | 31 / 48 | not counted: below the 55 the screen counts; see chapter IV |
| Finding in a parent | From | Lía | How we know |
|---|---|---|---|
| Cystic fibrosis carrier CFTR p.Phe508del | Elena | ● inherited | genotype |
| Cystic fibrosis carrier CFTR p.Gly542Ter | Marc | ○ not inherited | genotype |
| Fragile X intermediate repeat FMR1 | Elena | ● inherited, 48 → 49 | repeat length |
| Clopidogrel response CYP2C19 *2 | Marc | ● inherited, one copy | genotype |
| Phenylketonuria carrier PAH | Marc | ○ not inherited | genotype |
| Haemochromatosis carrier HFE | Elena | ○ not inherited | genotype |
| Hereditary breast and ovarian cancer BRCA2 | Elena | · ○ not inherited | |
Elena's longer FMR1 copy has 48 CGG repeats; the copy Lía received has 49. Both are intermediate: no disease, but it can grow a little each generation.
A one-repeat change is within the sizing error.
Both parents are RhD positive with one deleted RHD copy each. Lía received both deleted copies, a 1 in 4 outcome.
ABO: Elena A1, Marc O, Lía O. A prediction from DNA, not a lab typing.
Every child carries a few dozen new changes; most candidates found this way are reading errors. One passes the filters, and it sits outside any gene.
| Position | Change | Lía's reads | Depth L · M · E | Gene | Filter |
|---|---|---|---|---|---|
| chr7:98,114,350 | C>T | 46% alt | 33 · 30 · 35 | none nearby | passes |
| chr12:33,908,211 | A>G | 19% alt | 8 · 31 · 29 | none nearby | low: likely an error |
Two changes matter only when they sit on different copies (in trans) of a gene that fits. Neither pair here needs action.
| Gene | Changes | Copies | Reading |
|---|---|---|---|
| USH2A | p.Thr1257Ile · c.8559-14A>G | same copy, both from Marc | the other copy is intact |
| TTN | p.Arg3412His · p.Val16211Met | one from each parent | both benign or uncertain; TTN carries rare changes in everyone |