Minna Savukoski

CLN5 , a novel gene encoding a putative transmembrane protein mutated in Finnish variant late infantile neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs) represent a group of common recessive inherited neurodegenerative disorders of childhood, with an incidence of 1:12,500 live births. They are characterized by accumulation of autofluorescent lipopigments in various tissues. Several forms of NCLs have been identified, based on age at onset, progression of disease, neurophysiological and histopathological findings and separate genetic loci. All types of NCL cause progressive visual and mental decline, motor disturbance, epilepsy and behavioral changes, and lead to premature death. One of the subtypes, Finnish variant late infantile neuronal ceroid lipofuscinosis (vLINCL; MIM256731) affects children at 4–7 years of age. The first symptom is motor clumsiness, followed by progressive visual failure, mental and motor deterioration and later by myoclonia and seizures. We have previously reported linkage for vLINCL on chromosome 13 (ref. 5) and constructed a long-range physical map over the region. Here, we report the positional cloning of a novel gene, CLN5, underlying this severe neurological disorder. The gene encodes a putative transmembrane protein which shows no homology to previously reported proteins. Sequence analysis of DNA samples from patients with three different haplotypes revealed three mutations; one deletion, one nonsense and one missense mutation, suggesting that mutations in this gene are responsible for vLINCL.

Phenotype–genotype correlation in eight patients with Finnish variant late infantile NCL (CLN5)

Article abstract The authors analyzed the clinical phenotype, including MRI, of eight patients with Finnish variant late infantile neuronal ceroid lipofuscinosis (vLINCLFin; CLN5; MIM256731). Although the four known mutations, including one novel mutation identified in this study, have very different consequences for the predicted polypeptide, none of them results in an atypical phenotype, as has been reported in other forms of NCL. Thus, it seems likely that each mutation severely disturbs the normal function of the CLN5 protein.

Prenatally detected paternal uniparental chromosome 13 isodisomy

A 13q isodisomy in a balanced karyotype: 45, XY,‐13,‐13,+i(13)(q10) was found in cultured amniocytes studied because of advanced maternal age. The isochromosome was monocentric and a new mutation as both parents had normal chromosomes. Fetal blood was studied to exclude 13‐trisomy mosaicism. All (100) lymphocytes studied had the same karyotype with i(13)(q10) as the amniocytes. To determine the origin of the isochromosome, six microsatellite markers from 13q were analysed: D13S175, D13S166, D13S162, AC224, COLAC1 and D13S122. The results indicated that the i(13)(q10) was of paternal origin and isodisomic. The father had a risk of 1/20 for being a carrier for an autosomal recessive, progressive brain disorder, variant late infantile neuronal ceroid lipofuscinosis (CLN5). The risk for the fetus for this disorder of chromosome 13 was excluded by haplotype analysis. A healthy child was born at week 40 of pregnancy, supporting the idea that there are no paternally imprinted genes on chromosome 13q. Analysis of extra embryonal tissue (four samples studied) revealed the same balanced karyotype with the i(13)(q10)pat chromosome. According to the cytogenetic and molecular studies, the origin of the isochromosome 13 could be a transverse centromere cleavage at the paternal meiosis II or at an early mitosis. Copyright

6 Studies of homogenous populations: CLN5 and CLN8

Abstract Finland and the Finns have been the subject of numerous genetic and genealogical studies, owing to enrichment of certain rare hereditary disorders in the Finnish population. Two types of NCL have so-far been found almost exclusively in Finland: Finnish variant late infantile NCL, vLINCL (CLN5), and the Northern epilepsy syndrome or Progressive epilepsy with mental retardation, EPMR (CLN8). The first symptoms of Finnish vLINCL are concentration problems or motor clumsiness by 3 to 6 years of age, followed by mental retardation, visual failure, ataxia, myoclonus, and epilepsy. Northern epilepsy, the newest member of the NCL family with the most protracted course, is characterized by the onset of generalized seizures between 5 and 10 years of age and subsequent progressive mental retardation. Visual problems are slight and late, while myoclonus has not been observed. Both the Finnish vLINCL and Northern epilepsy are pathologically characterized by intraneuronal cytoplasmic deposits of autofluorescent granules which are Luxol fast blue-, PAS-, and Sudan black B-positive in paraffin sections. In Northern epilepsy the intraneuronal storage process and neuronal destruction are generally of mild degree but highly selective and, in contrast to other forms of childhood onset NCL, the cerebellar cortex is relatively spared. By electron microscopy the storage bodies mainly contain rectilinear complex type and fingerprints profiles in Finnish vLINCL and structures resembling curvilinear profiles in Northern epilepsy. Mitochondrial ATP synthase subunit c is the main stored protein in both disorders. Both the CLN5 and CLN8 genes encode putative membrane proteins with yet unknown functions. Furthermore, a well studied spontaneously occurring autosomal recessive mouse mutant, motor neuron degeneration (mnd) mouse, is a homolog for CLN8 .