Brazilian doc here. I live in a really poor part of an already poor country. When I was in my pediatric internship there was this baby wiith hepatomegaly (big liver). In my region, the first thing that you have to think about in this cases is a disease called Kala-Azar (also known as black fever or visceral leishmaniosis). It is an endemic disease which there is a parasite transmitted by a mosquito that can infect people with compromised immune system (like people living with HIV) and kids. This parasite infects the bone marrow and simulates clinical signs of acute leukemia, like chronic fever, spontaneous bruises and bleeding. The patient develops anemia, leukopenia (low white blood cells) and low platelets. To compensate, some organs like liver and spleen take care of the bone marrow function to create new blood cells, and thus, get bigger. This disease is really common in my region, but really rare in other parts, especially non-tropical countries like the US.
Anyway, as I was saying, this baby girl, about 1 year old was admitted to investigate a hepatomegaly. But the catch was that she kept having those episodes of hypoactivity and sleepiness, and sometimes even faintings that would then get better after she was being breastfed. We then checked and saw that she was having lots of hypoglycemia episodes. Her lab was normal,and she had no other clinical signs that would remind of kala-azar, besides the hepatomegaly.
The patient had Hers Disease, a genetic disorder that makes you produce less Glycogen due to an enzyme defect. Never hear of it before meeting this patient, and I think I'll never will meet other one.
Interestingly enough, in this same time, I had a patient that was admitted with leukopenia, anemia and low platelets that was also hospitalized to rule out Kala-Azar, but he actually had Fanconi Anemia, an also really rare genetic disease. In this one, the bone marrow slowly stops producing blood cells. Besides this, the patient also has kidney, facial, bones malformation and overall physical underdevelopment.