#615637
Table of Contents
A number sign (#) is used with this entry because of evidence that autosomal recessive intellectual disorder-41 (MRT41) is caused by homozygous or compound heterozygous mutation in the KPTN gene (615620) on chromosome 19q13.
Autosomal recessive intellectual developmental disorder-41 (MRT41) is characterized by macrocephaly and global developmental delay. Some patients have seizures (Baple et al., 2014).
Baple et al. (2014) reported 9 individuals from 4 nuclear Anabaptist Amish families from Ohio with an autosomal recessive intellectual developmental disorder. The patients had global developmental delay, mildly delayed walking, high levels of anxiety, stereotyped behavior, and repetitive speech. Dysmorphic features included macrocephaly (+3 to +5.4 SD) with frontal bossing, craniosynostosis, scaphocephaly, broad nasal bridge, hooded eyelids with small, downslanting palpebral fissures, and a prominent chin. Three patients had a seizure disorder, and 6 had childhood hypotonia. Less common features included fifth finger clinodactyly, recurrent pneumonia, and hepatosplenomegaly. Neuroimaging was unremarkable.
Pajusalu et al. (2015) reported 2 adult Estonian sibs with MRT41 apparent since early childhood. Both had normal early development, but presented with speech delay and intellectual disability at school age, resulting in special schooling. The brother had more severe behavioral abnormalities, including anxiety, autistic features, stereotypic movements, and some self-aggression. Both had macrocephaly (+4-4.5 SD), prominent forehead, high palate, and microretrognathia. The brother had a few isolated seizures in childhood, whereas the sister had no seizures. EEG in both patients showed generalized slowing of background activity. As adults, they lived in a special home for the intellectually disabled; they had basic self-care and communication skills.
Thiffault et al. (2020) reported a 9-year-old patient with MRT41 who presented with status epilepticus, macrocephaly, intractable epilepsy, autism, severe developmental delay, hypotonia, and hypoglycemia. He had dysmorphic features including frontal bossing, downslanting palpebral fissures, and small ears. He had a history of hepatosplenomegaly and hypoglycemic episodes at 5 months of age.
Pacio Miguez et al. (2020) reported 2 sisters, aged 7 and 3 years, with MRT41. The older sister presented at 3 years of age with speech and motor delay. At 7 years of age she had macrocephaly and expressive language impairment. The younger sister had progressive macrocephaly and speech delay at 3 years and 6 months of age. In both sibs, comprehensive language was less affected than expressive language, and they both had delayed closure of the anterior fontanel. A brain MRI in the younger sister showed nonspecific supratentorial leukoencephalopathy, and signal hyperintensity in the dentate nuclei. Neither sib had seizures.
The transmission pattern of MRT41 in the family reported by Baple et al. (2014) was consistent with autosomal recessive inheritance.
In 4 affected individuals from 2 consanguineous Amish families with autosomal recessive impaired intellectual development and macrocephaly, Baple et al. (2014) identified a homozygous truncating mutation in the KPTN gene (S259X; 615620.0001). The mutation was found using a combination of homozygosity mapping and whole-exome sequencing. Five affected individuals from 2 additional consanguineous Amish families were compound heterozygous for S259X and an in-frame duplication in the KPTN gene (615620.0002). All 4 families were determined to be distantly related, consistent with 2 founder mutations in this community. Transfection of the mutations into COS-7 cells showed that the mutant proteins did not localize like wildtype proteins to F-actin-rich lamellipodia, but rather accumulated at irregular perinuclear sites, suggesting a loss of normal activity. The truncated protein showed a more pronounced tendency to form such accumulations compared to the duplication mutation. Baple et al. (2014) suggested that the mutations resulted in a loss of KPTN function, which could lead to impairment of the neuronal actin cytoskeleton that is required for dendritic arborization or spine formation during neurogenesis.
In 2 Estonian sibs with MRT41, Pajusalu et al. (2015) identified a homozygous 1-bp duplication (c.665dupA; 615620.0003) in the KPTN gene, predicted to result in a frameshift (Gln222fs). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. Functional studies of the variant and studies of patient cells were not performed. The findings indicated that the disorder is not restricted to the Amish population.
In a 9-year-old Caucasian boy with MRT41, Thiffault et al. (2020) identified compound heterozygous mutations in the KPTN gene, a previously identified in-frame duplication (615620.0002) and a splice site mutation (615620.0004). The mutations were found by whole-genome sequencing and confirmed by Sanger sequencing. The splice site mutation but not the duplication was inherited from the mother, suggesting that the variants were in trans.
In 2 Spanish sibs with MRT41, Pacio Miguez et al. (2020) identified a homozygous 2-bp duplication in the KPTN gene (615620.0005). No information regarding segregation was provided.
Baple, E. L., Maroofian, R., Chioza, B. A., Izadi, M., Cross, H. E., Al-Turki, S., Barwick, K., Skrzypiec, A., Pawlak, R., Wagner, K., Coblentz, R., Zainy, T., Patton, M. A., Mansour, S., Rich, P., Qualmann, B., Hurles, M. E., Kessels, M. M., Crosby, A. H. Mutations in KPTN cause macrocephaly, neurodevelopmental delay, and seizures. Am. J. Hum. Genet. 94: 87-94, 2014. [PubMed: 24239382, images, related citations] [Full Text]
Pacio Miguez, M., Santos-Simarro, F., Garcia-Minaur, S., Velazquez Fragua, R., Del Pozo, A., Solis, M., Jimenez Rodriguez, C., Rufo-Rabadan, V., Fernandez, V. E., Rueda, I., Gomez Del Pozo, M. V., Gallego, N., Lapunzina, P., Palomares-Bralo, M. Pathogenic variants in KPTN, a rare cause of macrocephaly and intellectual disability. (Letter) Am. J. Med. Genet. 182A: 2222-2225, 2020. [PubMed: 32808430, related citations] [Full Text]
Pajusalu, S., Reimand, T., Ounap, K. Novel homozygous mutation in KPTN gene causing a familial intellectual disability-macrocephaly syndrome. Am. J. Med. Genet. 167A: 1913-1915, 2015. [PubMed: 25847626, related citations] [Full Text]
Thiffault, I., Atherton, A., Heese, B. A., T Abdelmoity, A., Pawar, K., Farrow, E., Zellmer, L., Miller, N., Soden, S., Saunders, C. Pathogenic variants in KPTN gene identified by clinical whole-genome sequencing. Cold Spring Harbor Molec. Case Stud. 6: a003970, 2020. [PubMed: 32358097, related citations] [Full Text]
Alternative titles; symbols
ORPHA: 397612; DO: 0081206;
Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
---|---|---|---|---|---|---|
19q13.32 | Intellectual developmental disorder, autosomal recessive 41 | 615637 | Autosomal recessive | 3 | KPTN | 615620 |
A number sign (#) is used with this entry because of evidence that autosomal recessive intellectual disorder-41 (MRT41) is caused by homozygous or compound heterozygous mutation in the KPTN gene (615620) on chromosome 19q13.
Autosomal recessive intellectual developmental disorder-41 (MRT41) is characterized by macrocephaly and global developmental delay. Some patients have seizures (Baple et al., 2014).
Baple et al. (2014) reported 9 individuals from 4 nuclear Anabaptist Amish families from Ohio with an autosomal recessive intellectual developmental disorder. The patients had global developmental delay, mildly delayed walking, high levels of anxiety, stereotyped behavior, and repetitive speech. Dysmorphic features included macrocephaly (+3 to +5.4 SD) with frontal bossing, craniosynostosis, scaphocephaly, broad nasal bridge, hooded eyelids with small, downslanting palpebral fissures, and a prominent chin. Three patients had a seizure disorder, and 6 had childhood hypotonia. Less common features included fifth finger clinodactyly, recurrent pneumonia, and hepatosplenomegaly. Neuroimaging was unremarkable.
Pajusalu et al. (2015) reported 2 adult Estonian sibs with MRT41 apparent since early childhood. Both had normal early development, but presented with speech delay and intellectual disability at school age, resulting in special schooling. The brother had more severe behavioral abnormalities, including anxiety, autistic features, stereotypic movements, and some self-aggression. Both had macrocephaly (+4-4.5 SD), prominent forehead, high palate, and microretrognathia. The brother had a few isolated seizures in childhood, whereas the sister had no seizures. EEG in both patients showed generalized slowing of background activity. As adults, they lived in a special home for the intellectually disabled; they had basic self-care and communication skills.
Thiffault et al. (2020) reported a 9-year-old patient with MRT41 who presented with status epilepticus, macrocephaly, intractable epilepsy, autism, severe developmental delay, hypotonia, and hypoglycemia. He had dysmorphic features including frontal bossing, downslanting palpebral fissures, and small ears. He had a history of hepatosplenomegaly and hypoglycemic episodes at 5 months of age.
Pacio Miguez et al. (2020) reported 2 sisters, aged 7 and 3 years, with MRT41. The older sister presented at 3 years of age with speech and motor delay. At 7 years of age she had macrocephaly and expressive language impairment. The younger sister had progressive macrocephaly and speech delay at 3 years and 6 months of age. In both sibs, comprehensive language was less affected than expressive language, and they both had delayed closure of the anterior fontanel. A brain MRI in the younger sister showed nonspecific supratentorial leukoencephalopathy, and signal hyperintensity in the dentate nuclei. Neither sib had seizures.
The transmission pattern of MRT41 in the family reported by Baple et al. (2014) was consistent with autosomal recessive inheritance.
In 4 affected individuals from 2 consanguineous Amish families with autosomal recessive impaired intellectual development and macrocephaly, Baple et al. (2014) identified a homozygous truncating mutation in the KPTN gene (S259X; 615620.0001). The mutation was found using a combination of homozygosity mapping and whole-exome sequencing. Five affected individuals from 2 additional consanguineous Amish families were compound heterozygous for S259X and an in-frame duplication in the KPTN gene (615620.0002). All 4 families were determined to be distantly related, consistent with 2 founder mutations in this community. Transfection of the mutations into COS-7 cells showed that the mutant proteins did not localize like wildtype proteins to F-actin-rich lamellipodia, but rather accumulated at irregular perinuclear sites, suggesting a loss of normal activity. The truncated protein showed a more pronounced tendency to form such accumulations compared to the duplication mutation. Baple et al. (2014) suggested that the mutations resulted in a loss of KPTN function, which could lead to impairment of the neuronal actin cytoskeleton that is required for dendritic arborization or spine formation during neurogenesis.
In 2 Estonian sibs with MRT41, Pajusalu et al. (2015) identified a homozygous 1-bp duplication (c.665dupA; 615620.0003) in the KPTN gene, predicted to result in a frameshift (Gln222fs). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. Functional studies of the variant and studies of patient cells were not performed. The findings indicated that the disorder is not restricted to the Amish population.
In a 9-year-old Caucasian boy with MRT41, Thiffault et al. (2020) identified compound heterozygous mutations in the KPTN gene, a previously identified in-frame duplication (615620.0002) and a splice site mutation (615620.0004). The mutations were found by whole-genome sequencing and confirmed by Sanger sequencing. The splice site mutation but not the duplication was inherited from the mother, suggesting that the variants were in trans.
In 2 Spanish sibs with MRT41, Pacio Miguez et al. (2020) identified a homozygous 2-bp duplication in the KPTN gene (615620.0005). No information regarding segregation was provided.
Baple, E. L., Maroofian, R., Chioza, B. A., Izadi, M., Cross, H. E., Al-Turki, S., Barwick, K., Skrzypiec, A., Pawlak, R., Wagner, K., Coblentz, R., Zainy, T., Patton, M. A., Mansour, S., Rich, P., Qualmann, B., Hurles, M. E., Kessels, M. M., Crosby, A. H. Mutations in KPTN cause macrocephaly, neurodevelopmental delay, and seizures. Am. J. Hum. Genet. 94: 87-94, 2014. [PubMed: 24239382] [Full Text: https://doi.org/10.1016/j.ajhg.2013.10.001]
Pacio Miguez, M., Santos-Simarro, F., Garcia-Minaur, S., Velazquez Fragua, R., Del Pozo, A., Solis, M., Jimenez Rodriguez, C., Rufo-Rabadan, V., Fernandez, V. E., Rueda, I., Gomez Del Pozo, M. V., Gallego, N., Lapunzina, P., Palomares-Bralo, M. Pathogenic variants in KPTN, a rare cause of macrocephaly and intellectual disability. (Letter) Am. J. Med. Genet. 182A: 2222-2225, 2020. [PubMed: 32808430] [Full Text: https://doi.org/10.1002/ajmg.a.61778]
Pajusalu, S., Reimand, T., Ounap, K. Novel homozygous mutation in KPTN gene causing a familial intellectual disability-macrocephaly syndrome. Am. J. Med. Genet. 167A: 1913-1915, 2015. [PubMed: 25847626] [Full Text: https://doi.org/10.1002/ajmg.a.37105]
Thiffault, I., Atherton, A., Heese, B. A., T Abdelmoity, A., Pawar, K., Farrow, E., Zellmer, L., Miller, N., Soden, S., Saunders, C. Pathogenic variants in KPTN gene identified by clinical whole-genome sequencing. Cold Spring Harbor Molec. Case Stud. 6: a003970, 2020. [PubMed: 32358097] [Full Text: https://doi.org/10.1101/mcs.a003970]
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