B. 1:2 – Explanation
In order to work out probability of inheritance, you need to know the disease inquestion.
This woman has neurofibromatosis. Neurofibromatosis is an autosomaldominant
condition therefore the chances of this woman’s child having the condition is50% or 1:2.
Neurofibromatosis
NF is a genetic disorder causing lesions in the skin, nervous system and skeleton.
Theneurofibromatoses are autosomal dominant genetic disorders that encompass the
rarediseases NF1, NF2, and schwannomatosis
Type 1 is the more common form
Type 2 is a central form with CNS tumours rather than skin lesions:
Schwannomatosis is a recently recognized form of neurofibromatosis, characterized
bymultiple non-cutaneous schwannomas, which is a histologically benign nerve
sheathtumour:
| A1 | A2 | A3 |
| B1 | B2 | B3 |
Diagnostic criteria for NF1
The diagnostic criteria for NF1 require at least two of seven criteria:
1. At least six café-au-lait spots or hyperpigmented macules
2. Axillary or inguinal freckles.
3. Two or more typical neurofibromas or one plexiform neurofibroma.
4. Optic nerve glioma.
5. Two or more iris hamartomas. They are called Lisch nodules and are seen by slit-
lamp examination.
6. Sphenoid dysplasia or typical long-bone abnormalities such as arthrosis.
7. Having a first-degree relative with NF1.
Knowing that neurofibromatosis is an autosomal dominant condition is important for
PLAB, as is knowing the difference between NF1 and NF2.
