We recently showed that mutations in the CNGA3 gene encoding the alpha-subunit of the cone photoreceptor cGMP-gated channel cause autosomal recessive complete achromatopsia linked to chromosome 2q11. We now report the results of a first comprehensive screening for CNGA3 mutations in a cohort of 258 additional independent families with hereditary cone photoreceptor disorders. CNGA3 mutations were detected not only in patients with the complete form of achromatopsia but also in incomplete achromats with residual cone photoreceptor function and (rarely) in patients with evidence for severe progressive cone dystrophy. In total, mutations were identified in 53 independent families comprising 38 new CNGA3 mutations, in addition to the 8 mutations reported elsewhere. Apparently, both mutant alleles were identified in 47 families, including 16 families with presumed homozygous mutations and 31 families with two heterozygous mutations. Single heterozygous mutations were identified in six additional families. The majority of all known CNGA3 mutations (39/46) are amino acid substitutions compared with only four stop-codon mutations, two 1-bp insertions and one 3-bp in-frame deletion. The missense mutations mostly affect amino acids conserved among the members of the cyclic nucleotide gated (CNG) channel family and cluster at the cytoplasmic face of transmembrane domains (TM) S1 and S2, in TM S4, and in the cGMP-binding domain. Several mutations were identified recurrently (e.g., R277C, R283W, R436W, and F547L). These four mutations account for 41.8% of all detected mutant CNGA3 alleles. Haplotype analysis suggests that the R436W and F547L mutant alleles have multiple origins, whereas we found evidence that the R283W alleles, which are particularly frequent among patients from Scandinavia and northern Italy, have a common origin.

Achromatopsia is a congenital, autosomal recessively inherited disorder characterized by a lack of color discrimination, low visual acuity (o0.2), photophobia, and nystagmus. Mutations in the genes for CNGA3, CNGB3, and GNAT2 have been associated with this disorder. Here, we analyzed the spectrum and prevalence of CNGB3 gene mutations in a cohort of 341 independent patients with achromatopsia. In 163 patients, CNGB3 mutations could be identified. A total of 105 achromats carried apparent homozygous mutations, 44 were compound (double) heterozygotes, and 14 patients had only a single mutant allele. The derived CNGB3 mutation spectrum comprises 28 different mutations including 12 nonsense mutations, eight insertions and/or deletions, five putative splice site mutations, and three missense mutations. Thus, the majority of mutations in the CNGB3 gene result in significantly altered and/or truncated polypeptides. Several mutations were found recurrently, in particular a 1 bp deletion, c.1148delC, which accounts for over 70% of all CNGB3 mutant alleles. In conclusion, mutations in the CNGB3 gene are responsible for approximately 50% of all patients with achromatopsia. This indicates that the CNGB3/ACHM3 locus on chromosome 8q21 is the major locus for achromatopsia in patients of European origin or descent.

Infants with cerebral palsy (CP) frequently present cerebral visual impairment (CVI) often caused by damage to retrochiasmatic pathways. This is particularly true of subjects with damage to the periventricular white matter. Thirty-eight preterm infants with periventricular leukomalacia (PVL) diagnosed by MRI were examined to correlate binocular visual acuity with neuroradiological findings. Binocular visual acuity was evaluated using Teller Acuity Cards and a complete ophthalmological examination was also performed. Three infants with ROP III were excluded from the sample. The age of observation ranged from 20 months to 5 and a half years (mean 42 months). The possible involvement of the optic radiations and/or of the calcarine cortex was detected by brain MRI. Twenty-three infants (66%) presented visual impairment. Of these, 9 (26%) were totally or nearly totally blind and 14 (40%) were low vision children. The other 12 (34%) had normal (2) or near normal (9) vision. MRI findings correlated with visual acuity; a relationship was detected between the degree of visual acuity and the reduction of the peritrigonal white matter, and also between the degree of visual acuity and the extent of calcarine atrophy. This report clearly establishes a relationship between visual impairment and specific MRI findings in children with PVL. Teller Acuity Cards and MRI are useful for detecting potential visual impairment and for improving both the clinical diagnosis of these disorders and the therapeutic approach to these subjects.

The aim of the study was to describe ocular motility in a sample of 56 patients affected by cerebral visual impairment (CVI) of hypoxic-ischemic origin. The sample consisted of 56 participants (37 males and 19 females), ranging in age from 2 to 16 years. In all cases CVI was associated with MRI-verified damage of the cerebral visual system. A complete ophthalmologic and neurological assessment was performed. Behaviour of gaze was studied in four conditions: during scanning of the surrounding environment, during fixation, execution of saccades, and pursuing. In addition, strabismus, nystagmus, and paroxysmal ocular deviations were evaluated. Ocular motility was studied by video recording the patients' eye motility during orthoptic examination. Each pattern of ocular motility studied revealed profound alterations in all the individuals examined. Typical features of ocular motility in CVI were: paroxysmal ocular deviations (present in 78%); the presence of variable angle strabismus (86%); and defective coordination of saccades (93%). Exploration of the environment and fixation were also impaired (88% and 84%, respectively). Disorders of initiation and performing saccades, absence of smooth pursuit, vergence abnormalities, nystagmus beats, instability of fixation, and difficulty in the systematic exploration of the environment were observed. These abnormalities characterize lack of gaze coordination found in children with brain damage. An early and detailed evaluation of ocular motility in individuals with CVI is important, especially when rehabilitation intervention is intended.