Congenital cataracts are common major abnormalities of the eye, which frequently cause blindness in infants . It may occur as an isolated anomaly, as part of generalized ocular development defects, or as a component of a multisystem disorder . In fact, association of cataract with congenital anomalies, mental retardation and microcephaly is reported in several cases with chromosomal anomalies and syndromes from genic origins [25–27].
Until today no candidate gene has been reported responsible for such phenotypes: association between congenital cataract, MR and congenital cataract, MR and microcephaly, so we tried to focus on genes already described in ADCC and/or ARCC and expressed in the human brain (PAX6, PITX3 and HSF4). And we chose to investigate the role of LIM2 gene in such phenotypes regarding the interaction between the proteins MP20 and galectin-3 in lens fiber cell.
MP20, a member of the tetraspanin superfamily, is the most abundant integral membrane protein of lens fiber cells, which appears to be distributed uniformly in the plasma membrane but also occurs in distinct membrane junctional domains early during embryonal development [9, 28–30].Mutations in MP20 severely disrupt normal crystalline fiber cell arrangement in the lens and cause cataractogenesis [7, 8, 31]. Tetraspanins form contacts with other cells or the extracellular matrix by binding to other tetraspanins, to adhesion receptors such as integrins, and to extracellular proteins [32–34]; in this context, recently MP20 and galectin-3 were identified to co-localize in selected areas of the cell plasma membrane and biochemical analysis confirmed that MP20 and galectin-3 interact with each other . In fact, galectin-3 is a multifunctional protein, which occurs early during embryonal development, with reported involvement in development, oncogenesis, and inflammation . It was found to be expressed by microglial cells , detected in a number of astrocytes in adult rat brain  and leads to injury in the deep gray matter areas of the brain . In addition, LIM2 has been implicated in autosomal recessive cataract and reported for the first time on 2002 by Pras and co-workers . By sequencing of LIM2, they revealed a Phe105Val mutation leading to a phenotype with a late-onset of cataract characterised by nuclear opacities, mild to moderate visual loss in three affected sibs whose healthy brother showed mental retardation with clear lens. On 2008, a second mutation Gly154Glu was reported by Ponnam and co-workers  in a phenotype involving congenital cataracts with severe visual impairment indicated by the presence of nystagmus and amblyopia but also with no sign of MR.
For PAX6 gene, it was first described as a candidate for human aniridia and ADCC but not for ARCC . PAX6 expression is not restricted to the eye and appears to be crucial for brain development . In order to elucidate this hypothesis, Dansault et al.  reported 14 affected members carrying a p.S74G mutation in exon 6 of PAX6 gene. All of them were suffering from diverse congenital ocular abnormalities including congenital cataracts, diverse neurological manifestations and variable cognitive impairments. Recently, Chien et al.  had identified a p.R317X PAX6 mutation in a patient (familial case) suffering from cataract, aniridia, nystagmus and was developmentally delayed. So these two reports proved that the PAX6 gene has a key role as a master regulator in the development of the eye and central nervous system.
As for PITX3, it was demonstrated to cause cataract and anterior segment mesenchymal dysgenesis (ASMD) in several families from different ethnic origins [41, 42]. It has been described only in ADCC but not in ARCC . Recently, Bidinost and coworkers (2006) reported one large Lebanese family where patients with a heterozygous mutation in PITX3 (650delG) had posterior polar cataracts (PPCs), while patients with the same mutation but with the homozygous state had a more severe ocular effect with severe microphthalmia associated with developmental delay and mental retardation. In addition, the two homozygous brothers are offspring of a consanguineous marriage, and their parents, who presented with PPCs, were examined through the 28 affected members and were heterozygous for the reported deletion. The neurologic phenotype of the homozygous patients implies an essential role for PITX3 in normal ocular and central nervous system development and this was the first report in which a potential new role of PITX3 in the development of the nervous system has been proved.
The last studied gene is HSF4 which was identified sufficiently important to lens development [44, 45] and disruption of the HSF4 gene leads to both autosomal dominant and ARCC (11-13). Bu et al.  reported, on 2002, four different missense mutations, within the HSF4 DNA binding domain, in patients with autosomal dominant lamellar and Marner cataracts from a large Chinese family. On 2004, Smaoui et al.  reported for the first time a HSF4 homozygous splice mutation in intron 12 (c.1327+4A>G) causing the skipping of exon 12 and leading to the installation of ARCC in a consanguineous Tunisian family. Then, Sajjad and coworkers  identified a novel HSF4 gene mutation (p.R405X) causing ARCC in a large consanguineous family from Pakistan. In the human, HSF4 is widely expressed, especially in the brain, heart, skeletal muscle, lung and pancreas [22, 23].
Taking these results further, we analysed LIM2, PAX6, PITX3 and HSF4 genes in four consanguineous Tunisian families with nine affected patients showing ARCC, MR for two brothers from F2 and ARCC, MR and microcephaly for the seven other patients belonging to the four families, but we did not identify any pathogenic mutation.
Only novel intronic variations; IVS2 -24A>G, IVS4 +32C>T, c.*15A>C detected in LIM2 gene, IVS4 -274insG, IVS12 -174G>A, IVS4 -195G>A identified in PAX6 gene and IVS7 +93C>T in HSF4 gene. And substitution polymorphisms; a reported one c.439 C>T (rs2281983) and a novel SNP c.930 C>A revealed respectively in exons 3 and 4 of PITX3 gene. These modifications did not segregate with studied phenotypes (ARCC, MR and ARCC, MR and microcephaly).
These findings did not exclude the role of LIM2, PAX6, PITX3 and HSF4 gene in both ocular and central nervous system but it underlined the fact that these transcription factors (PAX6, PITX3), heat-shock transcription factor (HSF4) and lens intrinsic membrane protein (LIM2) could not be responsible for the association between ARCC, MR and ARCC, MR and microcephaly in the four studied Tunisian families in spite of their expression in the human brain (PAX6, PITX3, HSF4) or their interaction with proteins expressed in human brain (LIM2).