Cataracts 13, Congenital, in Adult i RBC Phenotype

Clinical Characteristics
Ocular Features: 

The only ocular signs are dense nuclear cataracts with vision in the range of count fingers or light perception.  The opacities are usuallyrecognized at birth.  Some patients develop nystagmus. 

Systemic Features: 

The Ii blood group is associated with cataracts, most strongly in Asians.  The RBC antigens are developmentally regulated.  Fetal and neonatal RBCs express the i form of the antigen which is gradually converted enzymatically to the I form that normally persists in adults.  The normal Ii adult phenotype is reached before the age of two years. 

Genetics

Homozygous or compound heterozygous deletions of the GCNT2 gene (6p24.3) produce the adult i phenotype (110800) which may or may not be associated with lens opacities.

The GCNT2 gene codes for 3 variants of its product. Mutations that eliminate all 3 GCNT2 variants result in the adult i phenotype in association with congenital cataracts.

Treatment
Treatment Options: 

Surgery to remove the cataracts may be indicated in some individuals.

References
Article Title: 

Deletion at the GCNT2 Locus Causes Autosomal Recessive Congenital Cataracts

Irum B, Khan SY, Ali M, Daud M, Kabir F, Rauf B, Fatima F, Iqbal H, Khan AO, Al Obaisi S, Naeem MA, Nasir IA, Khan SN, Husnain T, Riazuddin S, Akram J, Eghrari AO, Riazuddin SA. Deletion at the GCNT2 Locus Causes Autosomal Recessive Congenital Cataracts. PLoS One. 2016 Dec 9;11(12):e0167562.

PubMed ID: 
27936067

References

Irum B, Khan SY, Ali M, Daud M, Kabir F, Rauf B, Fatima F, Iqbal H, Khan AO, Al Obaisi S, Naeem MA, Nasir IA, Khan SN, Husnain T, Riazuddin S, Akram J, Eghrari AO, Riazuddin SA. Deletion at the GCNT2 Locus Causes Autosomal Recessive Congenital Cataracts. PLoS One. 2016 Dec 9;11(12):e0167562.

PubMedID: 27936067

Yu LC, Lin M. Molecular genetics of the blood group I system and the regulation of I antigen expression during erythropoiesis and granulopoiesis. Curr Opin Hematol. 2011 Nov;18(6):421-6.  Review. 

PubMedID: 21912254

Yu LC, Twu YC, Chou ML, Reid ME, Gray AR, Moulds JM, Chang CY, Lin M. The molecular genetics of the human I locus and molecular background explain the partial association of the adult i phenotype with congenital cataracts. Blood. 2003 Mar 15;101(6):2081-8.

PubMedID: 12424189

Ogata H, Okubo Y, Akabane T. Phenotype i associated with congenital cataract in Japanese. Transfusion. 1979 Mar-Apr;19(2):166-8.

PubMedID: 432928