Molecular and clinical characterization of albinism in a large cohort of Italian patients.

PURPOSE: The purpose of this study was to identify the molecular basis of albinism in a large cohort of Italian patients showing typical ocular landmarks of the disease and to provide a full characterization of the clinical ophthalmic manifestations. METHODS: DNA samples from 45 patients with ocular manifestations of albinism were analyzed by direct sequencing analysis of five genes responsible for albinism: TYR, P, TYRP1, SLC45A2 (MATP), and OA1. All patients studied showed a variable degree of skin and hair hypopigmentation. Eighteen patients with distinct mutations in each gene associated with OCA were evaluated by detailed ophthalmic analysis, optical coherence tomography (OCT), and fundus autofluorescence. RESULTS: Disease-causing mutations were identified in more than 95% of analyzed patients with OCA (28/45 [62.2%] cases with two or more mutations; 15/45 [33.3%] cases with one mutation). Thirty-five different mutant alleles were identified of which 15 were novel. Mutations in TYR were the most frequent (73.3%), whereas mutations in P occurred more rarely (13.3%) than previously reported. Novel mutations were also identified in rare loci such as TYRP1 and MATP. Mutations in the OA1 gene were not detected. Clinical assessment revealed that patients with iris and macular pigmentation had significantly higher visual acuity than did severe hypopigmented phenotypes. CONCLUSIONS: TYR gene mutations represent a relevant cause of oculocutaneous albinism in Italy, whereas mutations in P present a lower frequency than that found in other populations. Clinical analysis revealed that the severity of the ocular manifestations depends on the degree of retinal pigmentation.

Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance.

We report that eight heterozygous missense mutations in TUBB3, encoding the neuron-specific beta-tubulin isotype III, result in a spectrum of human nervous system disorders that we now call the TUBB3 syndromes. Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy. Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts. A knock-in disease mouse model reveals axon guidance defects without evidence of cortical cell migration abnormalities. We show that the disease-associated mutations can impair tubulin heterodimer formation in vitro, although folded mutant heterodimers can still polymerize into microtubules. Modeling each mutation in yeast tubulin demonstrates that all alter dynamic instability whereas a subset disrupts the interaction of microtubules with kinesin motors. These findings demonstrate that normal TUBB3 is required for axon guidance and maintenance in mammals.

Sonic Hedgehog deletion and distal trisomy 3p in a patient with microphthalmia and microcephaly, lacking cerebral anomalies typical of holoprosencephaly.

About 20% of cases with 7q deletion syndrome is associated with holoprosencephaly (HPE), due to deletion of the Sonic Hedgehog (SHH) gene (mapping to 7q36). The occurrence of severe forms of holoprosencephaly is higher in cases of 7q deletion associated with partial trisomies involving different parts of the genomes than in patients with pure 7q deletion. All cases of 7q deletion associated with 3p duplication reported to date have been associated with severe forms of holoprosencephaly, and a gene(s) on distal 3p has (have) been hypothesized to be responsible for HPE phenotype when in triple dose. Here we describe a patient with unbalanced 3p;7q translocation, showing 7q deletion (including SHH gene) and 3p duplication (complete karyotype was 46,XY,der(7)t(3;7)(p26.3;q36.1)), presenting with a relatively mild phenotype, consisting of microphthalmia and microcephaly, without cerebral anomalies typical of holoprosencephaly. Possible involvement of some genes on 3p in determining such a mild phenotype is discussed.

Identification of KIF21A mutations as a rare cause of congenital fibrosis of the extraocular muscles type 3 (CFEOM3).

PURPOSE: Three congenital fibrosis of the extraocular muscles phenotypes (CFEOM1-3) have been identified. Each represents a specific form of paralytic strabismus characterized by congenital restrictive ophthalmoplegia, often with accompanying ptosis. It has been demonstrated that CFEOM1 results from mutations in KIF21A and CFEOM2 from mutations in PHOX2A. This study was conducted to determine the incidence of KIF21A and PHOX2A mutations among individuals with the third CFEOM phenotype, CFEOM3. METHODS: All pedigrees and sporadic individuals with CFEOM3 in the authors' database were identified, whether the pedigrees were linked or consistent with linkage to the FEOM1, FEOM2, and/or FEOM3 loci was determined, and the appropriate pedigrees and the sporadic individuals were screened for mutations in KIF21A and PHOX2A. RESULTS: Twelve CFEOM3 pedigrees and 10 CFEOM3 sporadic individuals were identified in the database. The structures of eight of the pedigrees permitted the generation of meaningful linkage data. KIF21A was screened in 17 probands, and mutations were identified in two CFEOM3 pedigrees. One pedigree harbored a novel mutation (2841G-->A, M947I) and one harbored the most common and recurrent of the CFEOM1 mutations identified previously (2860C-->T, R954W). None of CFEOM3 pedigrees or sporadic individuals harbored mutations in PHOX2A. CONCLUSIONS: The results demonstrate that KIF21A mutations are a rare cause of CFEOM3 and that KIF21A mutations can be nonpenetrant. Although KIF21A is the first gene to be associated with CFEOM3, the results imply that mutations in the unidentified FEOM3 gene are the more common cause of this phenotype.

Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1).

Congenital fibrosis of the extraocular muscles type 1 (CFEOM1; OMIM #135700) is an autosomal dominant strabismus disorder associated with defects of the oculomotor nerve. We show that individuals with CFEOM1 harbor heterozygous missense mutations in a kinesin motor protein encoded by KIF21A. We identified six different mutations in 44 of 45 probands. The primary mutational hotspots are in the stalk domain, highlighting an important new role for KIF21A and its stalk in the formation of the oculomotor axis.

Clinical and surgical data of affected members of a classic CFEOM I family.

BACKGROUND: Congenital fibiosis of the extraocular muscles (CFEOMI) refers to a group of congenital eye movement disorders that are characterized by non-progressive restrictive ophthalmoplegia. We present clinical and surgical data on affected members of a classic CFEOMI family. METHODS: Ten members of a fifteen-member, three-generation Italian family affected by classic CFEOM participated in this study. Each affected family member underwent ophthalmologic (corrected visual acuity, pupillary function, anterior segment and fundus examination), orthoptic (cover test, cover-uncover test, prism alternate cover test), and preoperative examinations. Eight of the ten affected members had surgery and underwent postoperative examinations. Surgical procedures are listed. RESULTS: All affected members were born with varying degrees of bilateral ptosis and ophthalmoplegia with both eyes fixed in a hypotropic position (classic CFEOM). The affected members clinical data prior to surgery, surgery procedures and postoperative outcomes are presented. On 14 operated eyes to correct ptosis there was an improvement in 12 eyes. In addition, the head position improved in all patients. CONCLUSIONS: Surgery is effective at improving ptosis in the majority of patients with classic CFEOM. However, the surgical approach should be individualized to each patient, as inherited CFEOM exhibits variable expressivity and the clinical features may differ markedly between affected individuals, even within the same family.

CFEOM1, the classic familial form of congenital fibrosis of the extraocular muscles, is genetically heterogeneous but does not result from mutations in ARIX.

BACKGROUND: To learn about the molecular etiology of strabismus, we are studying the genetic basis of 'congenital fibrosis of the extraocular muscles' (CFEOM). These syndromes are characterized by congenital restrictive ophthalmoplegia affecting muscles in the oculomotor and trochlear nerve distribution. Individuals with the classic form of CFEOM are born with bilateral ptosis and infraducted globes. When all affected members of a family have classic CFEOM, we classify the family as a CFEOM1 pedigree. We have previously determined that a CFEOM1 gene maps to the FEOM1 locus on chromosome 12cen. We now identify additional pedigrees with CFEOM1 to determine if the disorder is genetically heterogeneous and, if so, if any affected members of CFEOM1 pedigrees or sporadic cases of classic CFEOM harbor mutations in ARIX, the CFEOM2 disease gene. RESULTS: Eleven new CFEOM1 pedigrees were identified. All demonstrated autosomal dominant inheritance, and nine were consistent with linkage to FEOM1. Two small CFEOM1 families were not linked to FEOM1, and both were consistent with linkage to FEOM3. We screened two CFEOM1 families consistent with linkage to FEOM2 and 5 sporadic individuals with classic CFEOM and did not detect ARIX mutations. CONCLUSIONS: The phenotype of two small CFEOM1 families does not map to FEOM1, establishing genetic heterogeneity for this disorder. These two families may harbor mutations in the FEOM3 gene, as their phenotype is consistent with linkage to this locus. Thus far, we have not identified ARIX mutations in any affected members of CFEOM1 pedigrees or in any sporadic cases of classic CFEOM.