Importance of identifying the early ocular signs in clinching the diagnosis of a child with developmental delay, splenohepatomegaly and bicytopenia

A two and half year old female child, third born to third degree consanguineous parents with two other elder siblings being normal, was brought for evaluation of gross motor and language developmental delay, abnormal eye movements, and progressive upper abdominal distension for the past 1 year. There were no seizures or regression of milestones. On examination, the child was thin built with no obvious facial dysmorphism. There was marked pallor, but there was no icterus, significant lymphadenopathy, or edema. Her length, weight, and head circumference were less than −3Z scores for age and gender. Her vitals were normal. Head to toe examination revealed abnormal ocular gaze with marked abdominal distension. There was no evidence of bleeding manifestations or bony abnormalities. Abdominal examination revealed massive splenohepatomegaly. On ocular examination the child had mild ptosis. There was also bilateral esotropia with both the eyeballs fixed in adduction (Figure 1). There was restriction of horizontal and vertical eye movements indicating horizontal and vertical gaze palsy. The compromise in the vertical movement was compensated to some extent by the attempted upward movement of the head (Video 1). The child`s hearing was normal, and there was no other cranial nerve involvement except the oculomotor and the abducens nerves. There was mild generalized hypotonia with brisk deep tendon reflexes. Laboratory investigations revealed severe anemia with a hemoglobin of 57 g/L (requiring packed cell transfusion) and moderate thrombocytopenia (platelet count of 76000/microlitre) with normal leucocyte counts. What is the most probable diagnosis?