flat feet, prominent joints, dorsal kyphosis, sternal bulging, flaring of the rib cage, and awkward gait become evident. The deformities worsen with age.

Corneal clouding is a feature of Morquio syndrome. The corneal clouding in Morquio syndrome is relatively mild, having the appearance of a fine haze rather than the dense ground-glass opacification common to Hurler syndrome. The changes may not become clinically evident to the unaided eye for several years, often not before age 10 years.

Fundus abnormalities have been reported infrequently in Morquio syndrome. In most cases the fundi and light-adapted ERG are normal in MPS IV. Optic atrophy has been noted.

6.2.10.5  MPS VI: Maroteaux–Lamy Syndrome

The Maroteaux–Lamy syndrome (MPS VI) is characterized by severe dwarfism, visceromegaly, cardiac lesions, and progressive corneal clouding. In some cases hydrocephalus and spinal cord compression develop. Resembling the prototype mucopolysaccharidosis in many ways, the Maroteaux–Lamy syndrome is distinguished by retention of normal intellect, the pattern of mucopolysacchariduria, and the enzyme defect.

The principal ophthalmologic manifestation of MPS VI is progressive corneal clouding, usually evident within the first few years of life. The fundi in MPS VI generally are normal. As a rule, patients with Maroteaux–Lamy syndrome do not develop ophthalmoscopic signs of pigmentary retinal degeneration, and the ERG usually is normal.

6.2.10.6  MPS VII: Sly Syndrome

In the Sly syndrome (MPS VII), there is deficiency of b-glucuronidase, leading to a block in the degradation of dermatan sulfate and heparan sulfate, with urinary excretion of both dermatan sulfate and heparan sulfate. Clinical manifestations within the syndrome vary. The spectrum includes many of the characteristic features of mucopolysaccharidosis, including short stature, progressive skeletal deformity and radiologic signs of dysostosis multiplex, coarse facial features, hypertelorism, hepatosplenomegaly, diastasis recti, protuberant­ abdomen, hernias, intellectual impairment, cardiovascular involvement, and respiratory problems. In some

patients with Sly syndrome, the corneas are clear. Within the phenotypic variation of this disorder, however, corneal clouding may occur; this may be evident grossly or only on slit-lamp examination.

6.2.10.7  Abetalipoproteinemia

(Bassen–Kornzweig Syndrome)

Abetalipoproteinemia is an autosomal recessive disorder characterized by the absence b-lipoproteins from plasma. These b-lipoproteins, include low-density lipoproteins, very-low-density lipoproteins, and chylomicrons. Abetalipoproteinemia is caused by a defect in the MTTP gene which encodes for the microsomal triglyceride transfer protein, which is essential for formation of b-lipoproteins The deficiency of these lipoproteins prevents absorption through the digestive tract of dietary fats and fat-soluble vitamins such as vitamins E, A, and sometimes K. Fat malabsorption is severe and triglyceride accumulation occurs in enterocytes and liver. Affected children present in the first few months of life with failure to thrive, diarrhea, abnormal star-shaped red blood cells (acanthocytosis) andfatty,foul-smellingstools(steatorrhea).Impairment of neurologic function develops later in the course of the disease. Neurologic manifestations include spinocerebellar ataxia and peripheral neuropathy. Retinal degeneration was originally thought to be an inherent part of the disease process. Retinal pigmentary disturbances are now known to be secondary to vitamin E deficiency and should be preventable [35].

6.3  Disorders of Glycoprotein

6.3.1  Sialidosis

Sialadosis is an autosomal recessive disorder caused by a deficiency in neuraminidase activity. Two subtypes have been described: Type 1 is the less severe variant and Type 2 is more severe. A cherry-red spot may be seen in affected patients. Type 1 sialidosis has been called the cherry-red spot myoclonus syndrome [36]. Patients with type 1 sialidosis appear normal for the first two decades of life. They then develop visual and neurological problems. Neurological dysfunction