Wendy J. Introne

Phenotype and course of Hutchinson-Gilford progeria syndrome

BACKGROUND Hutchinson-Gilford progeria syndrome is a rare, sporadic, autosomal dominant syndrome that involves premature aging, generally leading to death at approximately 13 years of age due to myocardial infarction or stroke. The genetic basis of most cases of this syndrome is a change from glycine GGC to glycine GGT in codon 608 of the lamin A (LMNA) gene, which activates a cryptic splice donor site to produce abnormal lamin A; this disrupts the nuclear membrane and alters transcription. METHODS We enrolled 15 children between 1 and 17 years of age, representing nearly half of the worlds known patients with Hutchinson-Gilford progeria syndrome, in a comprehensive clinical protocol between February 2005 and May 2006. RESULTS Clinical investigations confirmed sclerotic skin, joint contractures, bone abnormalities, alopecia, and growth impairment in all 15 patients; cardiovascular and central nervous system sequelae were also documented. Previously unrecognized findings included prolonged prothrombin times, elevated platelet counts and serum phosphorus levels, measured reductions in joint range of motion, low-frequency conductive hearing loss, and functional oral deficits. Growth impairment was not related to inadequate nutrition, insulin unresponsiveness, or growth hormone deficiency. Growth hormone treatment in a few patients increased height growth by 10% and weight growth by 50%. Cardiovascular studies revealed diminishing vascular function with age, including elevated blood pressure, reduced vascular compliance, decreased ankle-brachial indexes, and adventitial thickening. CONCLUSIONS Establishing the detailed phenotype of Hutchinson-Gilford progeria syndrome is important because advances in understanding this syndrome may offer insight into normal aging. Abnormal lamin A (progerin) appears to accumulate with aging in normal cells. (ClinicalTrials.gov number, NCT00094393.)

A 3-year randomized therapeutic trial of nitisinone in alkaptonuria.

Alkaptonuria is a rare, autosomal recessive disorder of tyrosine degradation due to deficiency of the third enzyme in the catabolic pathway. As a result, homogentisic acid (HGA) accumulates and is excreted in gram quantities in the urine, which turns dark upon alkalization. The first symptoms, occurring in early adulthood, involve a painful, progressively debilitating arthritis of the spine and large joints. Cardiac valvular disease and renal and prostate stones occur later. Previously suggested therapies have failed to show benefit, and management remains symptomatic. Nitisinone, a potent inhibitor of the second enzyme in the tyrosine catabolic pathway, is considered a potential therapy; proof-of-principle studies showed 95% reduction in urinary HGA. Based on those findings, a prospective, randomized clinical trial was initiated in 2005 to evaluate 40 patients over a 36-month period. The primary outcome parameter was hip total range of motion with measures of musculoskeletal function serving as secondary parameters. Biochemically, this study consistently demonstrated 95% reduction of HGA in urine and plasma over the course of 3 years. Clinically, primary and secondary parameters did not prove benefit from the medication. Side effects were infrequent. This trial illustrates the remarkable tolerability of nitisinone, its biochemical efficacy, and the need to investigate its use in younger individuals prior to development of debilitating arthritis.

1,25-(OH)2D-24 Hydroxylase (CYP24A1) Deficiency as a Cause of Nephrolithiasis.

BACKGROUND AND OBJECTIVES Elevated serum vitamin D with hypercalciuria can result in nephrocalcinosis and nephrolithiasis. This study evaluated the cause of excess 1,25-dihydroxycholecalciferol (1α,25(OH)2D3) in the development of those disorders in two individuals. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Two patients with elevated vitamin D levels and nephrocalcinosis or nephrolithiasis were investigated at the National Institutes of Health (NIH) Clinical Center and the NIH Undiagnosed Diseases Program, by measuring calcium, phosphate, and vitamin D metabolites, and by performing CYP24A1 mutation analysis. RESULTS Both patients exhibited hypercalciuria, hypercalcemia, low parathyroid hormone, elevated vitamin D (1α,25(OH)2D3), normal 25-OHD3, decreased 24,25(OH)2D, and undetectable activity of 1,25(OH)2D-24-hydroxylase (CYP24A1), the enzyme that inactivates 1α,25(OH)2D3. Both patients had bi-allelic mutations in CYP24A1 leading to loss of function of this enzyme. On the basis of dbSNP data, the frequency of predicted deleterious bi-allelic CYP24A1 variants in the general population is estimated to be as high as 4%-20%. CONCLUSIONS The results of this study show that 1,25(OH)2D-24-hydroxylase deficiency due to bi-allelic mutations in CYP24A1 causes elevated serum vitamin D, hypercalciuria, nephrocalcinosis, and renal stones.

Mutation spectrum of homogentisic acid oxidase (HGD) in alkaptonuria

Alkaptonuria (AKU) is a rare autosomal recessive metabolic disorder, characterized by accumulation of homogentisic acid, leading to darkened urine, pigmentation of connective tissue (ochronosis), joint and spine arthritis, and destruction of cardiac valves. AKU is due to mutations in the homogentisate dioxygenase gene (HGD) that converts homogentisic acid to maleylacetoacetic acid in the tyrosine catabolic pathway. Here we report a comprehensive mutation analysis of 93 patients enrolled in our study, as well as an extensive update of all previously published HGD mutations associated with AKU. Within our patient cohort, we identified 52 HGD variants, of which 22 were novel. This yields a total of 91 identified HGD variations associated with AKU to date, including 62 missense, 13 splice site, 10 frameshift, 5 nonsense, and 1 no‐stop mutation. Most HGD variants reside in exons 3, 6, 8, and 13. We assessed the potential effect of all missense variations on protein function, using five bioinformatic tools specifically designed for interpretation of missense variants (SIFT, POLYPHEN, PANTHER, PMUT, and SNAP). We also analyzed the potential effect of splice‐site variants using two different tools (BDGP and NetGene2). This study provides valuable resources for molecular analysis of alkaptonuria and expands our knowledge of the molecular basis of this disease. Hum Mutat 30:1–9, 2009. Published 2009 Wiley‐Liss, Inc.

Exacerbation of the ochronosis of alkaptonuria due to renal insufficiency and improvement after renal transplantation.

In alkaptonuria, homogentisate 1,2-dioxygenase deficiency causes tissue accumulation of homogentisic acid (HGA), followed by signs and symptoms of ochronosis. These include massive urinary excretion of HGA, arthritis and joint destruction, pigmentation of cartilage and connective tissue, and cardiac valve deterioration. We describe a 46-year-old man with alkaptonuria and diabetic renal failure whose plasma HGA concentration was twice that of any other alkaptonuria patient, and whose ochronosis progressed much more rapidly than that of his two alkaptonuric siblings. After renal transplantation, the plasma HGA normalized, and the daily urinary excretion of HGA decreased by 2-3g. This case illustrates the critical role of renal tubular secretion in eliminating HGA from the body, and suggests that renal transplantation in a uremic patient not only restores HGA excretion, but may also provide homogentisate 1,2-dioxygenase activity for the metabolism of HGA.

Molecular Analysis of the Retinoic Acid Induced 1 Gene (RAI1) in Patients with Suspected Smith-Magenis Syndrome without the 17p11.2 Deletion

Smith-Magenis syndrome (SMS) is a complex neurobehavioral disorder characterized by multiple congenital anomalies. The syndrome is primarily ascribed to a ∼3.7 Mb de novo deletion on chromosome 17p11.2. Haploinsufficiency of multiple genes likely underlies the complex clinical phenotype. RAI1 (Retinoic Acid Induced 1) is recognized as a major gene involved in the SMS phenotype. Extensive genetic and clinical analyses of 36 patients with SMS-like features, but without the 17p11.2 microdeletion, yielded 10 patients with RAI1 variants, including 4 with de novo deleterious mutations, and 6 with novel missense variants, 5 of which were familial. Haplotype analysis showed two major RAI1 haplotypes in our primarily Caucasian cohort; the novel RAI1 variants did not occur in a preferred haplotype. RNA analysis revealed that RAI1 mRNA expression was significantly decreased in cells of patients with the common 17p11.2 deletion, as well as in those with de novo RAI1 variants. Expression levels varied in patients with familial RAI1 variants and in non-17p11.2 deleted patients without identified RAI1 defects. No correlation between SNP haplotype and RAI1 expression was found. Two clinical features, ocular abnormalities and polyembolokoilomania (object insertion), were significantly correlated with decreased RAI1 expression. While not significantly correlated, the presence of hearing loss, seizures, hoarse voice, childhood onset of obesity and specific behavioral aspects and the absence of immunologic abnormalities and cardiovascular or renal structural anomalies, appeared to be specific for the de novo RAI1 subgroup. Recognition of the combination of these features will assist in referral for RAI1 analysis of patients with SMS-like features without detectable microdeletion of 17p11.2. Moreover, RAI1 expression emerged as a genetic target for development of therapeutic interventions for SMS.

Atypical Chédiak-Higashi syndrome with attenuated phenotype: three adult siblings homozygous for a novel LYST deletion and with neurodegenerative disease.

BackgroundMutations in LYST, a gene encoding a putative lysosomal trafficking protein, cause Chédiak-Higashi syndrome (CHS), an autosomal recessive disorder typically characterized by infantile-onset hemophagocytic syndrome and immunodeficiency, and oculocutaneous albinism. A small number of reports of rare, attenuated forms of CHS exist, with affected individuals exhibiting progressive neurodegenerative disease beginning in early adulthood with cognitive decline, parkinsonism, features of spinocerebellar degeneration, and peripheral neuropathy, as well as subtle pigmentary abnormalities and subclinical or absent immune dysfunction.MethodsIn a consanguineous Pakistani kindred with clinical phenotypes consistent with attenuated CHS, we performed SNP array-based homozygosity mapping and whole gene sequencing of LYST.ResultsWe identified three individuals homozygous for a novel six base pair in-frame deletion in LYST (c.9827_9832ATACAA), predicting the loss of asparagine and threonine residues from the LYST transcript (p.Asn3276_Thr3277del), and segregating with the phenotype in this family.ConclusionsWe further characterize the neurologic features of the attenuated form of CHS, and discuss pathophysiologic mechanisms underlying the neurodegenerative components of CHS. Attenuated CHS is phenotypically heterogenous and should be considered when young adults develop neurodegenerative disease and have pigmentary abnormalities. We briefly discuss surveillance and management of patients with CHS-related neurodegeneration.

Chediak-Higashi syndrome presenting as young-onset levodopa-responsive parkinsonism

Chediak-Higashi syndrome (CHS) (OMIM #214500) is a rare autosomal recessive disorder caused by mutations in the lysosomal trafficking regulator gene, LYST, or CHS1. Typically, CHS presents, with variable degrees of oculocutaneous albinism, immunodeficiency, bleeding diathesis and hemophagocytic lymphohistiocytosis (HLH or the “accelerated phase”).1 Neurological involvement in CHS can include intellectual impairment, sensory-motor neuropathy, cerebellar disease, and dementia.2, 3 Parkinsonism and its response to dopaminergic therapy has rarely been reported.2,4,5 A subset of CHS patients have a muted pigmentary or hematological presentation while their neurological symptoms dominate their disease.6, 7 We a provide video illustration of his therapeutic response to levodopa along with skin pigment dilution features, brain imaging and leukocyte morphology in a young adult male with CHS whose clinical presentation is dominated by motor and non-motor parkinsonian symptoms with a brisk and sustained therapeutic response to levodopa therapy.

Aortic stenosis and vascular calcifications in alkaptonuria.

Alkaptonuria is a rare metabolic disorder of tyrosine catabolism in which homogentisic acid (HGA) accumulates and is deposited throughout the spine, large joints, cardiovascular system, and various tissues throughout the body. In the cardiovascular system, pigment deposition has been described in the heart valves, endocardium, pericardium, aortic intima and coronary arteries. The prevalence of cardiovascular disease in patients with alkaptonuria varies in previous reports. We present a series of 76 consecutive adult patients with alkaptonuria who underwent transthoracic echocardiography between 2000 and 2009. A subgroup of 40 patients enrolled in a treatment study underwent non-contrast CT scans and these were assessed for vascular calcifications. Six of the 76 patients had aortic valve replacement. In the remaining 70 patients, 12 patients had aortic sclerosis and 7 patients had aortic stenosis. Unlike degenerative aortic valve disease, we found no correlation with standard cardiac risk factors. There was a modest association between the severity of aortic valve disease and joint involvement, however, we saw no correlation with urine HGA levels. Vascular calcifications were seen in the coronaries, cardiac valves, aortic root, descending aorta and iliac arteries. These findings suggest an important role for echocardiographic screening of alkaptonuria patients to detect valvular heart disease and cardiac CT to detect coronary artery calcifications.

Chediak-Higashi syndrome: Lysosomal trafficking regulator domains regulate exocytosis of lytic granules but not cytokine secretion by natural killer cells

BACKGROUND Mutations in lysosomal trafficking regulator (LYST) cause Chediak-Higashi syndrome (CHS), a rare immunodeficiency with impaired cytotoxic lymphocyte function, mainly that of natural killer (NK) cells. Our understanding of NK cell function deficiency in patients with CHS and how LYST regulates lytic granule exocytosis is very limited. OBJECTIVE We sought to delineate cellular defects associated with LYST mutations responsible for the impaired NK cell function seen in patients with CHS. METHODS We analyzed NK cells from patients with CHS with missense mutations in the LYST ARM/HEAT (armadillo/huntingtin, elongation factor 3, protein phosphatase 2A, and the yeast kinase TOR1) or BEACH (beige and Chediak-Higashi) domains. RESULTS NK cells from patients with CHS displayed severely reduced cytotoxicity. Mutations in the ARM/HEAT domain led to a reduced number of perforin-containing granules, which were significantly increased in size but able to polarize to the immunologic synapse; however, they were unable to properly fuse with the plasma membrane. Mutations in the BEACH domain resulted in formation of normal or slightly enlarged granules that had markedly impaired polarization to the IS but could be exocytosed on reaching the immunologic synapse. Perforin-containing granules in NK cells from patients with CHS did not acquire certain lysosomal markers (lysosome-associated membrane protein 1/2) but were positive for markers of transport vesicles (cation-independent mannose 6-phosphate receptor), late endosomes (Ras-associated binding protein 27a), and, to some extent, early endosomes (early endosome antigen 1), indicating a lack of integrity in the endolysosomal compartments. NK cells from patients with CHS had normal cytokine compartments and cytokine secretion. CONCLUSION LYST is involved in regulation of multiple aspects of NK cell lytic activity, ranging from governance of lytic granule size to control of their polarization and exocytosis, as well as regulation of endolysosomal compartment identity. LYST functions in the regulated exocytosis but not in the constitutive secretion pathway.