Incidence
Monozygotic twinning occurs in birthing at a rate of about 3 in every 1000 deliveries worldwide (about 0.3% of the world population).The likelihood of a single fertilization resulting in monozygotic twins is uniformly distributed in all populations around the world. This is in marked contrast to dizygotic twinning, which ranges from about six per thousand births in Japan (almost similar to the rate of identical twins, which is around 4–5) to 15 and more per thousand in some parts of India and up to over 20 in some Central African countries. The exact cause for the splitting of a zygote or embryo is unknown. IVF techniques are more likely to create dizygotic twins. For IVF deliveries, there are nearly 21 pairs of twins for every 1,000. Genetic and epigenetic similarity
Monozygotic twins are genetically nearly identical and they are always the same sex unless there has been a mutation during development. The children of monozygotic twins test genetically as half-siblings (or full siblings, if a pair of monozygotic twins reproduces with another pair or with the same person), rather than first cousins. Identical twins do not have the same fingerprints however, because even within the confines of the womb, the fetuses touch different parts of their environment, giving rise to small variations in their corresponding prints and thus making them unique.Monozygotic twins always have the same genotype.
History
In 1956, Moshe Wolman, along with two other doctors, published the first case study of a LAL deficiency in a child born to closely related Persian Jews; 12 years later a case study on an older boy was published, which turned out to be the first case study of LAL-D.LAL-D was historically referred to as two separate disorders:

Wolman disease, presenting in infant patients
Cholesteryl Ester Storage Disease, presenting in pediatric and adult patientsAround 2010 both presentations have come to be known as LAL-D, as both are due to a deficiency of the LAL enzyme.In 2015 an enzyme replacement therapy, sebelipase alfa, was approved in the US and EU for the treatment of human LAL enzyme deficiency. Before the approval of that drug, as of 2009 the two oldest survivors of LAL-D in the world were then aged 4 and 11; both of them had been treated with hematopoietic stem cell treatment. Research directions
Some children with LAL-D have had an experimental therapy called hematopoietic stem cell transplantation (HSCT), also known as bone marrow transplant, to try to prevent the disease from getting worse. Data are sparse but there is a known high risk of serious complications including death, graft-versus-host disease. References
External links

National Organization for Rare Disorders (NORD)
Article - LYSOSOMAL ACID LIPASE/NIH.gov
Article - LYSOSOMAL ACID LIPASE DEFICIENCY/NIH.gov
Lipid Storage Diseases Fact Sheet at ninds.nih.gov