Abetalipoproteinaemia (ABL) and homozygousfamilial hypobetalipoproteinaemia (FHBL) arerare inherited disorders associated with low or undetectablelevels of apolipoprotein B (apoB)-containinglipoproteins. Patients present with the symptoms andsequelae of fat malabsorption, including fat-solublevitamin deficiencies. We describe two novel mutations:one an APOB gene mutation causing FHBL and theother a microsomal triglyceride transfer protein(MTP) gene mutation causing ABL. Two siblings ofconsanguineous parents were homozygous for an apoBmutation 4339delT causing an apoB–30.9 truncation. Inanother family, a boy born to consanguineous parentswas homozygous for a 319bp in-frame deletion of MTPexon 15 (c.2076–39_2303+52del319). All three childrenpresented with malabsorption and liver dysfunctionand had similar very low serum lipid, apoB, and fatsolublevitamin levels. The FHBL parents had lowserum lipid and apoB profiles distinguishing the disorderfrom the normal levels in ABL parents. Futurepatients presenting with FHBL or ABL should begenotyped to provide further insight into the varyingclinical severity related to molecular heterogenicity inthese two conditions.