**4. Fused in Sarcoma, Translocated in LipoSarcoma (FUS/TLS gene)**

Fused in Sarcoma, Translocated in LipoSarcoma (FUS/TLS) is a heterogeneous ribonucleo‐ protein (hnRNP) that is involved, as TARDBP, in RNA splicing, transportation and stabiliza‐ tion [38, 44]. FUS/TLS (fused in sarcoma/translocated in liposarcoma) was initially identified by investigators as a component of fusion proteins found in a variety of cancers such as myxoid liposarcoma, acute myeloid leukemia, and Ewing's tumour. More recently, researchers have found several mutations of FUS/TLS in ALS and FTLD (frontotemporal lobar degeneration) patients that causes cytoplasmic mislocalization of FUS/TLS.

#### **4.1. Genotype**

**3.2. Phenotype**

82 Current Advances in Amyotrophic Lateral Sclerosis

is only by chance.

Many individuals who present with a pure ALS phenotype also develop pathological features of FTD and vice versa. Recently TDP-43 is identified as the major protein of inclusions in FTD and ALS brain tissues, suggesting that both degenerative diseases belong to a clinio-patho‐ logical spectrum of overlapping central nervous system disorders. Dominant mutations in the

Corrado et al. [9] described 12 different missense mutations in TARDBP, all located in exon 6, in 18 patients with ALS, both FALS and SALS. Patients don't share a homogeneous clinical phenotype: the average age at onset is 53,2 +/- 14,5 years, the site of onset is mainly spinal (88%), disease duration varies from 17 to 87 months. But in contrast to what is expected from the similarity of TDP-43 pathological deposits in ALS and FTD, none of patients tested worldwide with FTD carried TARDBP mutations. On the contrary, a TARDBP mutation (p.G294V) is discovered in patients with ALS and dementia of Alzheimer type. He developed dementia 3 years before the onset of MND. It is possible that the concurrence of the two diseases

Piaceri et al. [42] described clinical heterogeneity in patients with ALS and mutations in TARDBP. Age at onset is between 49 and 62 years, site of onset is both spinal and bulbar with different involvement of upper or lower motor neuron, disease duration varies from 9 to 85

In literature also [9, 36] this mutation is associated with some differences in phenotype, that are in site of onset (bulbar-spinal in France and spinal in Italy), disease duration (28-73 months in France, 17-60 months in Italy) and age at onset (50 years in France, 32-69 years in Italy). Italian and French patients shared a common haplotype with allele D1S2667 and D1S489, so

Literature datas [43] suggested that in TARDBP patients site of onset is in the upper limbs, with both upper and lower motor neuron signs but with disease progression lower signs became predominant. Age at onset is mean of 54 years, disease duration mean of 58 months.

Fused in Sarcoma, Translocated in LipoSarcoma (FUS/TLS) is a heterogeneous ribonucleo‐ protein (hnRNP) that is involved, as TARDBP, in RNA splicing, transportation and stabiliza‐ tion [38, 44]. FUS/TLS (fused in sarcoma/translocated in liposarcoma) was initially identified by investigators as a component of fusion proteins found in a variety of cancers such as myxoid liposarcoma, acute myeloid leukemia, and Ewing's tumour. More recently, researchers have found several mutations of FUS/TLS in ALS and FTLD (frontotemporal lobar degeneration)

years. Nobody has FTD. One patient has p.ALA382Thr mutation in exon 6.

Some patients presented cognitive impairment that met criteria for FTD.

patients that causes cytoplasmic mislocalization of FUS/TLS.

**4. Fused in Sarcoma, Translocated in LipoSarcoma (FUS/TLS gene)**

there was a common founder for the mutation.

gene encoding the deposited protein account for at least some cases of these diseases.

The human *FUS/TLS* gene (Entrez Gene ID 2521) is located on chromosome 16p11.2, and it codes for a protein of 525 amino acids.

Mutations in *FUS/TLS* gene in ALS patients have been discovered for the first time in 2009 [37, 45], as *TARDBP*.

Following the original reports [37, 45], several other groups identified additional variants in ALS cohorts of different ethnicities, proposing an overall mutational frequency of ~4% in FALS and ~1% in SALS [46, 47, 48].

To date more than 30 different mutations have been described, the vast majority of which are missense substitutions and the rest are frameshift or nonsense mutations (Figure 3).

In the next year a Italian screening has been performed [10]. The results of the Italian screening are in accord with the interanation screening. The Italian data showed that the percentage of *FUS* missense mutations is 0.7% of Italian SALS cases, 4.4% in FALS.

**Figure 4.** Distribution of FUS mutations detected in sporadic ALS patients [41].

#### **4.2. Phenotype**

In 2010 Corrado et al. [10] identified 9 SALS or FALS patients carrying FUS missense mutations. Site of onset was both in upper and lower limbs, age at onset was lower (median 50 years). One of these patients with sporadic ALS and FUS mutation presented, at the age of 34, bilateral scapular girdle muscle weakness with unusual neck flexor/extensor muscle weakness with cramps and fasciculations, no weakness in the lower limbs has been demonstrated. Another patient with FALS and FUS mutation, at the age of 54, slowly developed weakness of the neck flexor/extensor muscles and bilateral scapular girdle and proximal upper limb muscle weakness, with subsequent impairment of the pelvic girdle, no bulbar involvement has been shown but slight proximal weakness in the lower limbs; one year after onset, the symptoms extended to the bulbar region. So these two patients developed an unusual proximal sym‐ metrical upper limbs onset and axial involvement.

Ticozzi N et al. in 2009 [49] described two patients with FALS and mutation of FUS that presented the same clinical phenotype.

In 2011 Lai SL et al. [50] described 4 Italian patients with sporadic ALS and FUS mutations (p.Y66Y, p.G507D, p.R521C, p.R521H). All of these cases initially manifested limb weakness and symptoms onset was before 50 years of age in more cases.

Patients with previously described I46V mutation presented distal weakness of lower limbs, predominance of LMN signs, slow course of disease (only in one case more rapid with bulbar

Genetics of ALS and Correlations Between Genotype and Phenotype in ALS — A Focus on Italian Population

http://dx.doi.org/10.5772/56547

85

So there was a wide phenotypic variability in these patients, for both district of onset and

Greenway et al. [53] reported that bulbar onset was more frequent in patients with ANG

Chromosome 9 open reading frame 72 is a protein localized on plasma membrane and cytoskeleton. There are two isoforms of C9orf72 that are produced as a result of alternative splicing events and the molecular weight of *C9orf72* isoforms is 54/25 kDa. Normally, it is

The human *C9orf72* gene (Entrez Gene ID 203228) is located on chromosome 9p21.2, and it

Recently, a hexanucleotide repeat expansion within the *C9orf72* gene was identified as the

About the Italian population, a screening *C9orf72* in a large cohort of 259 familial ALS, 1275 sporadic ALS, and 862 control individuals has been performed [12]. It has been found RE in 23.9% familial ALS, 5.1% sporadic ALS, and 0.2% controls. Two cases carried the RE together

Genotype data revealed that 95% of RE carriers shared a restricted 10-single nucleotide polymorphism haplotype within the previously reported 20-single nucleotide polymorphism risk haplotype, detectable in only 27% of nonexpanded ALS cases and in 28% of controls, suggesting a common founder with cohorts of North European ancestry. Although *C9orf72* RE segregates with disease, the identification of RE both in controls and in patients carrying additional pathogenic mutations suggests that penetrance and phenotypic expression of

Ratti et al. [12] observed that the phenotype of RE carriers was characterized in higher proportion by bulbar-onset compared with nonexpanded patients, while in individuals with spinal onset expanded patients displayed an early involvement of the upper limbs less frequently than other patients, with predominance of upper motor neuron signs. RE carriers had a shorter survival compared with noncarriers. There was a correlation between more frequent bulbar onset in expanded patients and shorter survival time. The concurrence of FTD

nuclear protein, even if the mutated form has been described in the cytoplasm [54].

involvement). Age at onset was between 50-60 years.

**6. Chromosome 9 open reading frame 72 (C9orf72)**

involvemenent of UMN/LMN.

codes for a protein of 481 amino acids.

cause of chromosome 9p21-linked ALS-FTD [54, 55].

*C9orf72* RE may depend on additional genetic risk factors.

with mutations in other ALS-associated genes.

mutations.

**6.1. Genotype**

**6.2. Phenotype**

In 2009 Chiò et al. [51] described a patient with mutation in FUS and a very young age at onset (<30 years) with a bulbar presentation and a short duration.

In literature [37, 45] confirmed this correlations between genotype and phenotype in FUS mutations in ALS both FALS and SALS patients.

Millecamps S et al. [43] suggested that FUS patients had a shorter lifespan, more rapid disease, younger onset than other mutations.
