congenital nystagmus

Congenital Nystagmus

Erik TwaroskiEye gifs from

<http://www.omlab.org>

CharacteristicsUncontrolled oscillation of the eyes

Onset at birth or within several months

1 in 1,500 live births

Patterns of inheritanceautosomal dominantautosomal recessiveX-linked dominantX-linked recessiveX-linked dominant with incomplete

penetrance

Genes involvedPAX6NYS1

PAX6 Highly conserved sequence

All known mutations involve a single change in the amino acid sequence

Positional cloning to determine area of genome (Hanson et al.) Maps to 11p13

Haploinsufficiency consistently present with all disorders associated with PAX6 Mutation in both copies is lethal

Thought to be the primary gene until recently

PAX6 (cont.)

Exons 4-13 contain coding regions. DNA binding domains and a linker.

PAX6 mutations

Sequence differences between normal and CN. Mutation creates a BsrI restriction site.

Picture from Hanson et al.

Mutation causing CN (Gly Val) shown in yellow at the N-terminal domain

PAX6 (cont.) Complete loss of PAX6 in mice is lethal

Knockouts cannot be made Elimination of one copy results is a

small eye phenotype

Picture from <http://www.mouse-genome.bcm.tmc.edu/ENU/publicimageview.asp>

Another gene?Until 1999 PAX6 was believed to be the

only gene responsible for CN All mutations resulted in eye disorders CN could only be linked to PAX6

NYS1Cabot et al. first to report mapping

CN to X chromosome Xp11.4-11.3 Dominant with incomplete penetrance

Important for eye developmentMajority of research done on this

gene

Picture from Cabot et al.

NYS1 (cont.)Started by finding microsatellites

on Xp Sequences known from the Genome

Database Regions of CA repeats

Recombination events indicated which markers were closely linked

Picture from Cabot et al.

Recombination events in parents of affected individuals

LOD scores for loci around NYS1

Picture from Cabot et al.

Support for location of an X-linked ICN gene, with respect to three chromosome Xp markers. Likelihood estimates are given in log10. Distances

between marker loci, in centimorgans, are shown along the X-axis. The maximum location score for NYS1 is between DXS8015 and DXS1003, over the locus DXS993.

Picture from Cabot et al.

More statistical analysis

Map of Xp

Based on this NYS1 is between DXS8015 and DXS1003 (18.6-

cM)

X-inactivation pattern between normal and carrier/affected

Skewed X-inactivation patterns in affected haplotype or unaffected haplotype

TreatmentsCurrently no treatments availableCN does not appear to interfere

with visual function.Dell’Osso and Jacobs characterized

the ocular oscillations of CN over a 35 year study published in July 2004

Treatments (cont.)Dell’Osso and Jacobs found that

the body is able to compensate Even the most severe cases showed

signs of some compensationMore research needs to be

conducted to further understand how the body is able to compensate

Questions?

References1. Annick Cabet, Jean-Michel Rozet, Sylvie Gerber, Isabelle Perrault,

Dominique Ducroq, Asmae Smahi, Eric Souied, Arnold Munnich, and Josseline Kaplan. “A Gene for X-Linked Idiopathic Congenital Nystagmus (NYS1) Maps to Chromosome Xp11.4-p11.3.” American Journal of Human Genetics 64:1141-1146, 1999.

2. Isabel Hanson, Amanda Churchill, James Love, Richard Axton, Tony Moore, Michael Clarke, Francoise Meire, and Veronica van Heyningen. “Missense mutations in the most ancient residues of the PAX6 paired domain underlie a spectrum of human congenital eye malformations.” Human Molecular Genetics, 1999, Vol. 8, No. 2.

3. Jonathan B. Jacobs and Louis F. Dell’Osso. “Congenital nystagmus: Hypotheses for its genesis and complex waveforms within a behavioral ocular motor system model.” Journal of Vision 4: 604-625, 2004.

4. Sanjaya Singh, Lian Y. Chao, Rajnikant Mishra, Jonathan Davies, and Grady F. Saunders. “Missense mutation at the C-terminus of PAX6 negatively modulates homeodomain function.” Human Molecular Genetics, 2001, Vol. 10, No. 9.