The penetrance of AIP is incomplete with only 10% of gene carriers experiencing acute attacks suggesting role for other modifying genes or environment.The exact mechanism of acute attacks is not clear. The most favored hypothesis is that porpholobilinogen buildup causes a toxic effects on neurons. The autonomic and peripheral nervous system are more vulnerable than the central nervous system because they are not protected by the blood-brain barrier. This explains findings such as abdominal pain and tachycardia. Some individuals may be more likely to develop paresis based on increased susceptibility of neurons to toxins. Genetics
Inheritance
AIP has an autosomal dominant pattern of inheritance. The dominance pattern is a result of partial deficiencies from the heme biosynthesis enzymes, hydroxymethylbilane synthase  (HMBS;  EC  2.5.1.61). Due to the rarity of this disease it is difficult to estimate the prevalence of AIP and the inclusion criteria differs widely among studies causing varying statistics. AIP has a low penetrance when considering the general population, but within families the penetrance increases. This is indicative of another interaction affecting the inheritance pattern. It is speculated that this pattern is due to AIP propensity caused by the inheritance of an additional gene mutation, HMBS, in addition to other genetic and environmental influences. There have been 421 HMBS mutations that have been linked to AIP. This suggests that AIP inheritance instead follows an oligogenic or polygenic inheritance pattern.
classified this tumour into two subtypes: 

1) medulloepithelioma not otherwise specified
2) medulloepithelioma with differentiation into astrocytes, oligodendrocytes; ependymal cells; neuronal cells; others (melanin, mesenchymal cells); and mixed cellular elements. Treatment
Total resection of the tumour, followed by radiation therapy is the standard treatment modality. Medulloepithelioma of the ciliary body may necessitate enucleation of the eye. Radiation therapy alone may prolong survival. Aggressive chemotherapy with autologous bone marrow transplant is used for metastatic medulloepitheliomas. Prognosis
Medulloepithelioma carries a dismal prognosis with a median survival of 5 months. Epidemiology
Medulloepithelioma most commonly affect children between 6 months and 5 years; rarely, this tumour may occur congenitally or beyond this age range. Incidence is equal in males and females. References


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