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Microcoria is the most consistent ocular feature but is not present in some families. It is congenital and sometimes seen with iris hypoplasia. Glaucoma and lens opacities (including posterior lenticonus sometimes) are present in one-fourth of patients. Corneal size varies with some patients having apparent macrocornea which can lead to the mistaken diagnosis of buphthalmos. Pigment mottling and clumping is common in the retina and the ERG can show changes characteristic of cone-rod dystrophy. Retinal thinning is often present as well. Non-rhegmatogenous retinal detachments occur in 24% of patients and optic atrophy is seen in some patients. There is considerable interocular, intrafamilial, and interfamilial variability in these signs.
The primary and most consistent systemic problem is progressive renal disease. Congenital nephrotic syndrome with proteinuria, hypoalbuminemia and hypertension is characteristic. Renal failure eventually occurs although the rate of progression varies. Most patients require a renal transplant for end-stage kidney disease in the first decade of life. Kidney histology shows glomerulosclerosis, peritubular scarring, and diffuse mesangial sclerosis. Hypotonia and muscle weakness are sometimes present and congenital myasthenia has been reported. Severe global psychomotor retardation is common and many infants never achieve normal milestones.
This is an autosomal recessive disorder resulting from homozygous mutations in the LAMB2 gene located at 3p21. The normal gene encodes laminin beta-2 that is strongly expressed in intraocular muscles which may explain the hypoplasia of ciliary and pupillary muscles in Pierson syndrome. Mutations in this gene are often associated with nephronophthisis but ocular abnormalities are not always present.
Kidney replacement can restore renal function. Glaucoma, cataracts, and retinal detachments require the usual treatment but patient selection is important due to the neurological deficits. Lifelong monitoring is essential.