Early hematopoietic stem cell transplantation in a patient with severe mucopolysaccharidosis II: A 7 years follow-up

Abstract

Mucopolysaccharidosis type II (MPS II - Hunter syndrome) is an X-linked lysosomal storage disorder caused by a deficiency in the enzyme iduronate-2 sulfatase (I2S), leading to the accumulation of the glycosaminoglycans, affecting multiple organs and systems. Enzyme replacement therapy does not cross the blood brain barrier, limiting results in neurological forms of the disease. Another option of treatment for severe MPS, hematopoietic stem cell transplantation (HSCT) has become the treatment of choice for the severe form of MPS type I, since it can preserve neurocognition when performed early in the course of the disease. To date, only few studies have examined the long-term outcomes of HSCT in patients with MPS II. We describe the seven-year follow-up of a prenatally diagnosed MPS II boy with positive family history of severe MPS form, submitted to HSCT with umbilical cord blood cells at 70 days of age. Engraftment after 30 days revealed mixed chimerism with 79% donor cells; after 7 years engraftment remains at 80%. I2S activity 30 days post-transplant was low in plasma and normal in leukocytes and the same pattern is observed to date. At age 7 years growth charts are normal and he is very healthy, although mild signs of dysostosis multiplex are present, as well as hearing loss. The neuropsychological evaluation (Wechsler Intelligence Scale for Children - Fourth Edition - WISC-IV), disclosed an IQ of 47. Despite this low measured IQ, the patient continues to show improvements in cognitive, language and motor skills, being quite functional. We believe that HSCT is a therapeutic option for MPS II patients with the severe phenotype, as it could preserve neurocognition or even halt neurodegeneration, provided strict selection criteria are followed.

Keywords: Hematopoietic stem cell transplantation; Mucopolysaccharidosis; Neurocognition.

Fig. 1

Transplanted MPS II patient at age 7 years. (A): no joint stiffness. (B) no MPS phenotype. (C) no claw hands.

Fig. 2

Mild Dysostosis Multiplex in the transplanted MPS II boy. (A) Hands: shortened and proximal pointing of metacarpals, hypoplasia of carpals. (B) Pelvis: round iliac wings and inferior iliac tapering (C) Long bones: defect of linear growth with thick shortened diaphyses. (D) Skull: thickened calvaria. (E) Spine: inferiorly beaked vertebrae and platyspondyly in lumbar spine.

Fig. 3

Clinical phenotype of the propositus (A), his older brother (B) and uncle (C) at age of 6 years. The propositus at age 4 years and his brother at age 12 years (D).The propositus at age 7 years and his uncle at age 20 years (E).

Fig. 4

Propositus' uncle at 7 years. X-Ray images showing signs of severe dysostosis multiplex in the hand (A) - proximal pointing of metacarpals, shortened metacarpals and carpal hypoplasia - and spine (B) - abnormal modeling and inferiorly beaked vertebrae. Cranial computed tomography (C) and (D) showing enlargement of the supratentorial ventricles and cortical atrophy, even after shunting.