A patient tells you he/she (or his/her partner) has a relative with an intellectual disability (ID).
There are numerous causes of intellectual disability and it might not be possible to identify a cause. Many families have been given diagnoses in the past which are erroneous. The Clinical Genetics team can only give advice when a diagnosis is confirmed by medical notes (+/- laboratory test).
The closer the relationship to the individual with ID, the higher the risk that the couple may have an affected child.
Intellectual disability can be due to:
- non genetic causes, or
- genetic causes
The genetic causes can be due to a:
- chromosomal anomaly, or
- single gene anomaly
Both of these anomalies can occur as a sporadic event (new mutation) in a family with negligible recurrence risk to at-risk relatives. However, some inherited forms can occur (chromosomal translocations, X-linked genes causing ID in males etc), so there may be a risk to your patient.
NCMG advice in this scenario is to determine:
- who was affected in the family and how they are related to the couple in the antenatal clinic?
- was the affected individual(s) a male or female?
If your patient is concerned and you need advice, we will need details (name, date of birth) of the affected relative(s). We can then search to see if there are any records of the affected cases and outcomes would be as follows:
- If we could find no records- we cannot help. Depending on the pedigree structure we could give an estimate on recurrence risks (after weighing up all possible modes of inheritance)
- The records are found but indicate that no diagnosis had been reached. Depending on the pedigree structure we could give an estimate on recurrence risks (after weighing up all possible modes of inheritance). We might suggest more updated tests on the affected individual that could be offered, but this is only appropriate if your patient is the parent of an affected child. We cannot re-investigate other people’s children (to help establish their relative recurrence risk) without their consent.
- The records are found and NCMG is able to establish a diagnosis from the records. Under these circumstances, we would be able to give accurate risks to your patient. Ultimately, this could mean (1) Negligible risk to your patient; no tests required; reassure your patient, (2) increased risk established; NCMG will advise accordingly and arrange assessment