Abstract Meniere’s disease (MD) is an inner ear disorder characterized by vertigo, tinnitus and sensorineural hearing impairment. An inherited form of the disease is called familial Meniere’s disease (FMD). The aim of this thesis was to describe the clinical and genetic features of Finnish FMD and to study its prevalence in Finland. In addition genetic factors previously associated with MD were studied in Finnish MD patients. A total of 38 Meniere-families were analysed in this study. In most of the families the mode of inheritance was found to be autosomal dominant. Meniere-like symptoms such as tinnitus or vertigo were common in these families even in individuals without a full triad of MD. Familial patients were affected earlier, suffered from longer spells of vertigo and had more autoimmune diseases compared to sporadic MD patients. The prevalence of FMD was studied among the patients treated in the Oulu University Hospital and Kainuu Central Hospital during the years 2005-2010. A family history of MD was probable in 23.4% of the cases, but only 9.3% could be confirmed, as it was not possible to gain information from deceased generations. Six candidate genes previously associated with MD were screened for mutations in Finnish MD patients. Two possibly adverse variations were observed in the KCNE1 gene in two patients but in none of the controls. The role of these variations in MD is still unclear and needs further study. The association of MD to the five other genes could not be confirmed, nor was Finnish FMD linked to a previously suggested locus on chromosome 12. / Tiivistelmä Menieren tauti on sisäkorvan sairaus, jolle on tyypillistä huimaus, korvien soiminen ja kuulon heikkeneminen. Tauti voi esiintyä myös perinnöllisenä. Tutkimustyön tavoitteena oli selvittää perinnöllisyyden osuutta Menieren taudissa, kuvata suomalaisen perinnöllisen Menieren taudin tyypilliset piirteet ja tutkia suomalaisessa aineistossa aikaisemmin tautiin yhdistettyjä perinnöllisiä tekijöitä. Tutkimuksessa analysoitiin 38 sukua, joissa Menieren tautia esiintyi perinnöllisenä. Suurimmassa osassa tapauksista periytyminen tapahtui vallitsevasti. Suvuissa esiintyi paljon Meniere-tyypistä oirehdintaa, kuten tinnitusta ja huimausta, ilman Menieren taudin koko taudinkuvaa. Meniere-suvuissa potilaat sairastuivat keskimääräistä aikaisemmin, kärsivät pidemmistä huimauskohtauksista ja sairastivat enemmän autoimmuunitauteja. Perinnöllisen Menieren taudin yleisyyttä tutkittiin Kainuun keskussairaalassa ja Oulun yliopistollisessa sairaalassa vuosina 2005−2010 hoidettujen potilaiden keskuudessa. Potilaista 23,4 %:lla Menieren taudin sukuhistoria oli positiivinen; kuitenkin vain 9,3 % pystyttiin vahvistamaan, sillä tietojen kerääminen edesmenneiltä sukupolvilta ei ollut mahdollista. Kuuden Menieren tautiin aikaisemmin yhdistetyn geenin merkitystä tutkittiin suomalaisessa aineistossa mutaatio- ja ehdokasgeenianalyysillä. KCNE1-geenistä löydettiin kaksi mahdollisesti proteiinia vaurioittavaa sekvenssinvaihtelua, joita ei havaittu kontrollihenkilöillä. Muutosten merkitys Menieren taudin synnyssä jäi kuitenkin epävarmaksi ja vaatii jatkotutkimuksia. Muiden geenien yhteyttä sairauteen ei pystytty vahvistamaan. Suomalainen Menieren tauti ei myöskään kytkeytynyt aikaisemmin ehdotettuun lokukseen kromosomissa 12.

<p>Positional cloning is a method to identify genes from their position in the genome without prior knowledge about function. We used this approach to investigate the basis for three distinct genetic disorders; Obesity, Ichthyosis Prematurity Syndrome and Meniere's disease.</p><p>Obesity appears when energy intake exceeds energy expenditure which leads to an abnormal accumulation of fat in the adipocyte tissue. We have studied a family with a balanced chromosomal translocation t(4;15) segregating with severe obesity. The chromosomal breakpoints create a fusion gene involving the gene for isoform 1 of RAR-related orphan receptor A (<i>RORa1</i>) which is implicated in the regulation of adipogenesis and lipoprotein metabolism. We hypothesize that the obesity in this family is caused by haploinsufficiency of this gene or a gain of function of the fusion gene.</p><p>Ichthyosis prematurity syndrome (IPS) is a rare skin disorder belonging to a group of autosomal recessive congenital ichthyosis. We have mapped the locus for IPS to chromosome 9q34. Within the IPS locus, we identified a core haplotype with a high carrier frequency among affected, which indicate a possible founder mutation for the disease. The minimal shared region in affected patients contains seven genes which are candidates for IPS.</p><p>Meniere's disease (MD) is characterised by spontaneous attacks of vertigo, fluctuating sensorineural low frequency hearing loss, aural fullness, and tinnitus. We mapped the MD locus to chromosome 12p13 using three Swedish families. The linked region is 463 kb, containing only one gene, a phosphoinositide-3-kinase (<i>PIK3C2G</i>). Involvement of phosphatidylinositol 3-kinases (PI-3K) in the intra cellular signalling cascades of cells in mammalian balance epithelia makes this gene a good candidate gene for MD.</p>

<p>Monogenic disorders offer a possibility for studies of genetic disturbances in hearing impairment—a knowledge which could be essential for development of future treatment options. In this thesis, the underlying genetic disturbances in neurofibromatosis 2 (NF2) and familial Meniere’s disease (FMD) were evaluated, and familial X-linked hearing impairment was described from a clinical point of view. </p><p>In paper I, constitutional DNA from 116 individuals with NF2 of variable severity was studied using the array-CGH method focusing on a 7.6-Mb area surrounding the NF2 gene on chromosome 22q. Deletions were found in 20.7% of samples. In mild NF2, the deletions were small, but variable sizes of deletions were found in cases that were moderately or severely affected. Disease phenotype could not be predicted from the size of the deletions.</p><p>In papers II and III, a single five-generation family with autosomal dominant FMD was described. Anticipation concerning age of onset was observed. Genome scan revealed five candidate gene regions with a LOD score of > 1. Two additional families with autosomal dominant MD were analyzed for linkage to these five regions. A cumulative Zmax of 3.46 was obtained for a single 463-kb region on chromosome 12p12.3, containing only one known gene: PIK3C2G. This encodes a protein with a proposed role in hair cell regeneration in mammalian ears. No mutations were found in protein-coding sequences or exon-intron borders. In two of the three families, a shared haplotype, suggested common ancestry, was found to extend over 1.7 Mb, which could be a genomic region of importance for FMD.</p><p>In paper IV, a family in which five males displayed progressive low- and mid-frequency hearing impairment from the first or second decade was described. Female carriers were affected by a high-frequency hearing impairment from the fourth decade. The family could represent a novel X-linked dominant audiophenotype.</p>

Positional cloning is a method to identify genes from their position in the genome without prior knowledge about function. We used this approach to investigate the basis for three distinct genetic disorders; Obesity, Ichthyosis Prematurity Syndrome and Meniere's disease. Obesity appears when energy intake exceeds energy expenditure which leads to an abnormal accumulation of fat in the adipocyte tissue. We have studied a family with a balanced chromosomal translocation t(4;15) segregating with severe obesity. The chromosomal breakpoints create a fusion gene involving the gene for isoform 1 of RAR-related orphan receptor A (RORa1) which is implicated in the regulation of adipogenesis and lipoprotein metabolism. We hypothesize that the obesity in this family is caused by haploinsufficiency of this gene or a gain of function of the fusion gene. Ichthyosis prematurity syndrome (IPS) is a rare skin disorder belonging to a group of autosomal recessive congenital ichthyosis. We have mapped the locus for IPS to chromosome 9q34. Within the IPS locus, we identified a core haplotype with a high carrier frequency among affected, which indicate a possible founder mutation for the disease. The minimal shared region in affected patients contains seven genes which are candidates for IPS. Meniere's disease (MD) is characterised by spontaneous attacks of vertigo, fluctuating sensorineural low frequency hearing loss, aural fullness, and tinnitus. We mapped the MD locus to chromosome 12p13 using three Swedish families. The linked region is 463 kb, containing only one gene, a phosphoinositide-3-kinase (PIK3C2G). Involvement of phosphatidylinositol 3-kinases (PI-3K) in the intra cellular signalling cascades of cells in mammalian balance epithelia makes this gene a good candidate gene for MD.

Monogenic disorders offer a possibility for studies of genetic disturbances in hearing impairment—a knowledge which could be essential for development of future treatment options. In this thesis, the underlying genetic disturbances in neurofibromatosis 2 (NF2) and familial Meniere’s disease (FMD) were evaluated, and familial X-linked hearing impairment was described from a clinical point of view. In paper I, constitutional DNA from 116 individuals with NF2 of variable severity was studied using the array-CGH method focusing on a 7.6-Mb area surrounding the NF2 gene on chromosome 22q. Deletions were found in 20.7% of samples. In mild NF2, the deletions were small, but variable sizes of deletions were found in cases that were moderately or severely affected. Disease phenotype could not be predicted from the size of the deletions. In papers II and III, a single five-generation family with autosomal dominant FMD was described. Anticipation concerning age of onset was observed. Genome scan revealed five candidate gene regions with a LOD score of &gt; 1. Two additional families with autosomal dominant MD were analyzed for linkage to these five regions. A cumulative Zmax of 3.46 was obtained for a single 463-kb region on chromosome 12p12.3, containing only one known gene: PIK3C2G. This encodes a protein with a proposed role in hair cell regeneration in mammalian ears. No mutations were found in protein-coding sequences or exon-intron borders. In two of the three families, a shared haplotype, suggested common ancestry, was found to extend over 1.7 Mb, which could be a genomic region of importance for FMD. In paper IV, a family in which five males displayed progressive low- and mid-frequency hearing impairment from the first or second decade was described. Female carriers were affected by a high-frequency hearing impairment from the fourth decade. The family could represent a novel X-linked dominant audiophenotype.