Mucolipidosis II (ML II)

Mucolipidosis II (ML II) is a rare, inherited disorder that is progressive in nature and affects many of the body’s systems. Mucolipidosis II is also known as I-cell disease. The condition is classified as a lysosomal storage disorder (LSD). In these disorders, genetic variations disrupt the normal activity of lysosomes in human cells.

Lysosomes in human cells contain specific proteins known as enzymes that are responsible for breaking down and recycling molecules such as fats and sugars. Individuals with a lysosomal storage disorder lack one of these necessary enzymes or do not contain one of these enzymes in sufficient quantities to break down molecules for cells to function properly.

Children born with mucolipidosis II are often small at birth. They often have a weak cry and poor muscle tone (hypotonia). As infants, they grow slowly until their physical development often plateaus around 24 months of age.

Children with mucolipidosis II may also have symptoms such as:

• Delayed physical development
• Delayed cognitive development
• Delayed motor skills
• Skeletal abnormalities
• Abdominal or umbilical hernia
• Joint abnormalities
• Distinct facial features (coarse facial features)

Other symptoms children might experience over time include:

• Hoarse voice due to vocal cord stiffening
• Frequent respiratory infections
• Frequent ear infections leading to hearing loss
• Excessive growth of the gums (gingival hyperplasia)

Mucolipidosis II is caused by a mutation in a gene called GNPTAB, which results in the deficiency of the enzyme GlcNAc-1-phosphotransferase, which lysosomes require to properly break down large molecules inside the body’s cells. This genetic condition is inherited in an autosomal recessive pattern, which means that an affected child has received one defective copy of the GNPTAB gene from each of their parents.

There are currently no approved therapies to reverse the effects of mucolipidosis II. Current approaches involve managing specific symptoms through targeted therapies and collaboration between specialists.

At the Boston Children’s Lysosomal Storage Disorder (BoLD) Program, our team of providers is committed to the care of complex patients. As part of Boston Children’s Hospital, we are prepared to meet the challenge of providing multifaceted care by partnering with you and your child to deliver direct care in our BoLD clinic We work with the broad array of world-class specialists at Boston Children’s to optimize the care we provide your child with mucolipidosis II.