Extreme degree familial hypobetalipoproteinemia caused by hypothetic double heterozygosity in a subject with severe mental deficiency

: We described the case of an adult male patient, seriously mentally deficient, hospitalised in Psychiatric Hospital for a period of many years, suffering from a familial hypobetalipoproteinemia with extremely low levels of plasmatic betalipoproteins. The patient has been followed and tested several times over a period of six years. Numerous members of his family, which is part of a restricted ethnic nucleus in a locality (Iolo) of the Comune of Prato in the Provincia of Florence, were examined and tested too. Consanguinity between his parents is not demonstrable. The diagnosis of homozygous hypobetalipoproteinemia is discarded, but it does not seem that the heterozygous one is to be accepted as weel. On the ground of the existence of two syndromes which are quite unlike each other, but both explainable as form of familial heterozygous hypobetalipoproteinemia, one of them present in his father, the other one in his mother and in the maternal relatives as in the patient's brother respectively, a hypothesis of a double heterozygosis could be formulated. Extant is the support of the recent literature data, depending on them the possibility of making the hypothesis of a multiplicity of the genes regulating the apolipoprotein B synthesis. We do not exclude that the peculiarity of the event of a double heterozygosis can also be directly responsible of the patient's serious mental deficiency, being at the same time more supportable the hypothesis of a encephalopathy in his early childhood.