Heterozygous and Homozygous Variants in SORL1 Gene in Alzheimer's Disease Patients: Clinical, Neuroimaging and Neuropathological Findings

In the last few years, the SORL1 gene has been strongly implicated in the development of Alzheimer’s disease (AD). We performed whole-exome sequencing on 37 patients with early-onset dementia or family history suggestive of autosomal dominant dementia. Data analysis was based on a custom panel that included 46 genes related to AD and dementia. SORL1 variants were present in a high proportion of patients with candidate variants (15%, 3/20). We expand the clinical manifestations associated with the SORL1 gene by reporting detailed clinical and neuroimaging findings of six unrelated patients with AD and SORL1 mutations. We also present for the first time a patient with the homozygous truncating variant c.364C>T (p.R122*) in SORL1, who also had severe cerebral amyloid angiopathy. Furthermore, we report neuropathological findings and immunochemistry assays from one patient with the splicing variant c.4519+5G>A in the SORL1 gene, in which AD was confirmed by neuropathological examination. Our results highlight the heterogeneity of clinical presentation and familial dementia background of SORL1-associated AD and suggest that SORL1 might be contributing to AD development as a risk factor gene rather than as a major autosomal dominant gene.

Mutations in TRIM63 cause an autosomal-recessive form of hypertrophic cardiomyopathy

OBJECTIVE

Up to 50% of patients with hypertrophic cardiomyopathy (HCM) show no disease-causing variants in genetic studies. TRIM63 has been suggested as a candidate gene for the development of cardiomyopathies, although evidence for a causative role in HCM is limited. We sought to investigate the relationship between rare variants in TRIM63 and the development of HCM.

METHODS

TRIM63 was sequenced by next generation sequencing in 4867 index cases with a clinical diagnosis of HCM and in 3628 probands with other cardiomyopathies. Additionally, 3136 index cases with familial cardiovascular diseases other than cardiomyopathy (mainly channelopathies and aortic diseases) were used as controls.

RESULTS

Sixteen index cases with rare homozygous or compound heterozygous variants in TRIM63 (15 HCM and one restrictive cardiomyopathy) were included. No homozygous or compound heterozygous were identified in the control population. Familial evaluation showed that only homozygous and compound heterozygous had signs of disease, whereas all heterozygous family members were healthy. The mean age at diagnosis was 35 years (range 15-69). Fifty per cent of patients had concentric left ventricular hypertrophy (LVH) and 45% were asymptomatic at the moment of the first examination. Significant degrees of late gadolinium enhancement were detected in 80% of affected individuals, and 20% of patients had left ventricular (LV) systolic dysfunction. Fifty per cent had non-sustained ventricular tachycardia. Twenty per cent of patients suffered an adverse cerebrovascular event (20%).

CONCLUSION

TRIM63 appears to be an uncommon cause of HCM inherited in an autosomal-recessive manner and associated with concentric LVH and a high rate of LV dysfunction.

Cystinuria in a patient with 19q12q13.1 deletion

Cystinuria is a genetic cause of kidney stones with a prevalence of 1 in 7000 births. So far, two genes have been described responsible for this disorder (SLC3A1 and SLC7A9). We report a patient with an SLC7A9 gene mutation located in 19q13.1 on one allele and with a 19q12q13 region deletion on the other allele. The characteristic clinical features of the 19q13.1 microdeletion syndrome include facial dysmorphism, signs of ectodermal dysplasia, growth retardation, neurologic features and genitourinary anomalies. Cystinuria has not yet been described as part of this syndrome, although one of its responsible genes (SLC7A9) is in the same genomic location. The index case is a 6-year-old male presented with distinctive facial features, cutis aplasia of the scalp, rudimentary teeth, microcephaly, intrauterine and postnatal growth retardation, psychomotor developmental delay, speech delay, epilepsy, inguinal hernias and cystinuria. An array-CGH analysis was performed, finding a large deletion of the 19q12q13.11 cytobands, which affects 19 genes. Two of them are involved in the 19q13.11 deletion syndrome and another affected gene is SLC7A9, responsible for type B cystinuria. Sanger sequencing was performed as well, detecting a heterozygous mutation of the SLC7A9 gene, located in 19q13.1. As far as we know, this is the first described case of cystinuria in a patient with SLC7A9 gene mutation located in 19q13.1 on one allele and with 19q12q13 region deletion on the other allele. Although this patient can be classified as a type B heterozygote and, therefore, his renal prognosis is not severe, the occasional nephrolithiasis found in such patients justifies a close follow-up with regular testing of urinary cystine excretion. We suggest that the recessive behavior of this case, explains the clinical features regarding cystinuria. We propose that in the face of patients affected of a phenotype matchable with 19q13.11 syndrome and cystinuria, a mutational or sequencing study of the SLC7A9 gene should be performed to allow an early onset of diagnosis and treatment.

Alport Syndrome: De Novo Mutation in the COL4A5 Gene Converting Glycine 1205 to Valine

BACKGROUND

Alport syndrome is a primary basement membrane disorder arising from mutations in genes encoding the type IV collagen protein family. It is a genetically heterogeneous disease with different mutations and forms of inheritance that presents with renal affection, hearing loss and eye defects. Several new mutations related to X-linked forms have been previously determined.

METHODS

We report the case of a 12 years old male and his family diagnosed with Alport syndrome after genetic analysis was performed.

RESULT

A new mutation determining a nucleotide change c.3614G > T (p.Gly1205Val) in hemizygosis in the COL4A5 gene was found. This molecular defect has not been previously described.

CONCLUSION

Molecular biology has helped us to comprehend the mechanisms of pathophysiology in Alport syndrome. Genetic analysis provides the only conclusive diagnosis of the disorder at the moment. Our contribution with a new mutation further supports the need of more sophisticated molecular methods to increase the mutation detection rates with lower costs and less time.

Alport Syndrome: De Novo Mutation in the COL4A5 Gene Converting Glycine 1205 to Valine

Background

Alport syndrome is a primary basement membrane disorder arising from mutations in genes encoding the type IV collagen protein family. It is a genetically heterogeneous disease with different mutations and forms of inheritance that presents with renal affection, hearing loss and eye defects. Several new mutations related to X-linked forms have been previously determined.

Methods

We report the case of a 12 years old male and his family diagnosed with Alport syndrome after genetic analysis was performed.

Result

Anew mutation determining a nucleotide change C.3614G > T (p. Gly1205Val) in hemizygosis in the COL4A5 gene was found. This molecular defect has not been previously described.

Conclusion

Molecular biology has helped us to comprehend the mechanisms of pathophysiology in Alport syndrome. Genetic analysis provides the only conclusive diagnosis of the disorder at the moment. Our contribution with a new mutation further supports the need of more sophisticated molecular methods to increase the mutation detection rates with lower costs and less time.