A few days ago, I was dealing with an unhealthy amount of bubble-wrap - well, it is Christmas season and I have figured out that the best Christmas present is the quintessential mug featuring Rudolph and his friends prancing in the snow. Anyway, due to prevailing lockdown restrictions and my commitments, I've decided not to deliver the gift in person. Instead, I've opted, with a heavy heart, to rely on the postal service. It's not that I never bestow them the trust they expect from me, it's just that I've got stuff missed in the post several times already. My last Christmas present (to someone special) got smashed when admixed with large parcel boxes. This brings me to using the legendary bubble-wrap film, reminiscing how, as a kid, I used to squish the bubbles as prime entertainment.
I was reminded of a particular condition I saw in the wards. It was one of the very absurd and weird ones that do not deviate from the norm much in terms of clinical presentation. However, once you discover more about the internal manifestation through radiology and pathology, you would realise you've hit the jackpot. For medical bumblebees, from apprenticeship all the way to masterhood, there is always a flicker of joy whenever a rare diagnosis pops up. Common things do come first, but they are also likely to be mundane and routine.
Before I start, I want to refresh our memory on the anatomy of the liver as well as the structures nearby, just so we can understand later, the case of the 'liver encased in bubble-wrap film'.
Anatomy of Liver and Co.:
This diagram shows the anatomical structures of the liver. Of note, the porta hepatis is comparable to the hilum of the lung, providing the portal of access for the following structures: the portal hepatic vein, hepatic artery, lymph nodes, nerve endings (vagus nerve) and the common hepatic duct. This diagram also shows the position of the gallbladder, which is tucked into the undersurface of the liver. Recalling from the article on gallbladder disease and pancreatitis, the gallbladder does not produce bile juice. It stores and concentrates it instead. This diagram is extracted from: https://healthjade.com/wp-content/uploads/2017/10/Liver-anatomy.jpg.
This diagram shows the surgical anatomy of the liver. There are two models of anatomy in many organs, one being the liver (another example would be the anatomical vs surgical necks of the humerus). The surgical anatomy leads to the dissection of the liver into eight sections, where segment 1 is the caudate lobe (inferior to which is the quadrate lobe). The surgical classification is also known as the Couinaud Classification. The diagram is extracted from: https://i.pinimg.com/originals/26/6e/b7/266eb735f10413cb1ab5791c4126bbfa.png.
This diagram shows the liver and its anatomical relations with the pancreas, gallbladder, bile ducts and the duodenum. This diagram is extracted from: https://childrensgimd.com/wp-content/gallery/digestive-system/liver-gall-bladder-pancreas.jpg.
As seen from the diagrams above, the liver is entrammelled in an intricate network of anatomical relations and is often lauded as the most important organ in the body. More so, considering the fact that the hepatic portal vein receives blood from many parts of the gastrointestinal system. It runs parallel to the systemic circulation, facilitated by the inferior vena cava receiving drainage from different structures within the genitourinary system and from below the pectinate line of the anal canal.
This is a normal CT scan of the abdomen, showing the liver, the two lovely kidneys, the antrum of the stomach, as well as the small bowel. The hypodense lesion (as compared to the liver) encapsulated in the liver is supposedly the gallbladder. As tempting as it might, it is not a sign of hepatocellular carcinoma (even then, we need to look at the phase of the contrast).This diagram is extracted from Radiopaedia.
The Case:
Lucinda Jane** is a 54-year old woman, born and bred in Shanghai (China) (the point will become obvious soon), whom I've seen in the liver transplantation ward. This is already a bias since it indicates the patient does have a liver condition (otherwise why would she be in a liver transplantation ward?). The patient is G1P1 and post-menopausal. She has first presented to the clinic complaining of abdominal pain, post-prandial fullness, jaundice (observed by family members) and pruritus. As usual, let's dive into the case by first introducing the patient profile.
Patient Profile:
CHIEF COMPLAINTS & PRESENTING FEATURES:
Jaundice - first noticed three weeks ago by family members and staring at herself in the mirror; persistent and progressive in temporality, with no previous episodes identifiable; greenish jaundice in terms of quality; no identifiable ameliorating or exacerbating circumstances;
Abdominal Pain - over the right upper quadrant, no radiation elsewhere; pain severity graded at 5-6 / 10 on the Visual Analogue Scale; dull in quality; progressive in nature and first noticed three months ago; persistent and showed no improvement throughout; there are no identifiable factors of amelioration or exacerbation;
Epigastric Symptoms: These are quintessentially related to the stomach which are present in this patient. They are first noticed one month ago and get progressively serious. The patient complains of post-prandial fullness, early satiety, and belching.
Pruritus: First started two weeks ago; generalised in scope, persistent and progressively serious, to the extent of affecting quality of life and severe annoyance; no amelioration of symptoms via the application of emollients or any other topical medication; no exacerbating factor identified.
The patient is constantly anorexic and fatigued. This has been the way for the past few weeks.
There are no anaemic symptoms.
Review of systems reveals nothing else significant. Crucially, there is no haematemesis or vomiting. Nor are there any issues with defaecation. Faecal matter is also normal in consistency (Bristol Stool Chart) and colour. There are no changes in bowel habit.
Haematemesis and dried blood in stool (tarry stool) may indicate the presence of oesophageal varices. Fresh blood on stool, rectal fullness and constipation may indicate the presence of haemorrhoids. Both conditions are related to portal hypertension, which can be induced by a liver condition.
PAST MEDICAL & SURGICAL HISTORY:
No hypertension, no diabetes mellitus;
No known history of Hepatitis B or Hepatitis C infection;
No known HIV and Tuberculosis status;
No known congenital issues, including and especially glycogen storage diseases;
No known history of biliary disorders, including gallstones.
No known history of coagulopathies.
DRUG HISTORY: unremarkable - no chronic medication taken, no recreational drug use and no known drug allergies;
AUTOIMMUNE HISTORY: Asthmatic, but well-controlled and the patient has not been bothered by the condition for over twenty-three years (thus has not been using medication, i.e. inhaled salbutamol).
FAMILY HISTORY: Father also developed greenish jaundice and was diagnosed alcoholic liver disease, having died from liver failure subsequently; Mother is generally healthy, except for Hepatitis B which is well-controlled by taking entecavir. Married and husband does not have any known chronic medical conditions. This includes Hepatitis B, Hepatitis C, HIV, tuberculosis and coagulopathies.
SOCIAL HISTORY:
The patient has never smoked or consumed alcohol in her life (convinced by her mother that she is allergic to alcohol and has never had a sip in her life - we have to take the patient's word for it);
Born and bred in Shanghai, China and moved to the UK three years ago and did not go anywhere since. This means the patient has never once left the country for the past three years (again, bear with me, this is significant);
Living with family and they are supportive (this makes it easier when it comes to rehabilitation, reintegration and treatment compliance). No other family member under the same household has presented with similar symptoms (aka no clustering);
No known life stressors which require psychiatric or medical attention;
Diet unremarkable and the patient regularly exercises (at least an hour of jogging every day, for the past twenty years);
PAST OBSTETRICS & GYNAECOLOGY HISTORY: (basically important in all women) Unremarkable. No complications related to prior pregnancy and labour.
Physical Examination:
In light of the patient's symptoms and clinical history, I've decided to perform a full abdominal examination, general examination and digital rectal examination (I don't have a choice).
Comments on General Exam-
Vital Signs: Temperature - 36 degrees (non-feverish), BMI - 21.2 kg/m2; Heart Rate- 89 beats per minute, Respiratory Rate- 16 breaths per minute, Blood Pressure- 127 / 82 mmHg, no changes in urinary output and urinalysis is unremarkable;
The patient is generally irritated, seen scratching incessantly. There are no issues related to consciousness. GCS = 15 / 15. Hepatic encephalopathy is unlikely upon observation. The patient is jaundiced (greenish), which is seen all over the skin and the sclera. There is no pallor. The patient's pulses are symmetrical, regular in rhythm and normal in rate (as above). The carotid pulses are normal in volume.
Liver-related Signs: The patient has finger clubbing. The patient has mild peripheral oedema. The patient also has scratch marks across the abdomen and the medial aspects of her forearms. The patient also has bruises over the left upper quadrant of the abdomen and right supraclavicular fossa. The patient is negative for (a) telangiectasia and spider naevi, (b) palmar erythema, (c) hepatic flap, (d) Dupuytren's contracture, (e) caput medusa, and (f) leuconychia.
Clinical Picture showing Caput Medusa in a jaundiced patient with abdominal distension. Caput medusa is a sign of portal hypertension, which can mean an underlying liver disease, although other aetiologies include heart failure and splenic vein thrombosis. The clinical picture is extracted from: https://qph.fs.quoracdn.net/main-qimg-205d5b4a2f152aae98738deaa67e3532.
This clinical picture shows Dupuytren's Contracture, which is usually associated with alcoholic liver disease. Note the thickened digital tendons leading to restrained digital movement. It is extracted from WebMD.
In the interests of the patient, upon noticing the bruises, I've asked about the patient's family to see if there are any subtle clues that might indicate domestic violence. I can detect no signs and assume that the bruises are medical in origin.
Lymph Node Examination: Unremarkable.
Diagrams illustrating the abdominal regions (a) and quadrants (b). The diagrams are extracted from: https://emedicalupdates.com/wp-content/uploads/2017/11/abdominal-quadrants-anatomy-regions-image-photo-picture.jpg.
Comments on Abdominal Exam-
Inspection: There is abdominal distension. Bruises and scratch marks are present as mentioned afore. From observation, the liver seems enlarged - this will be elucidated in respective sections below. No other masses or scars (virgin abdomen) are seen. The skin is jaundiced, as mentioned above.
Abdominal Palpation:
Superficial palpation yields pain over the right upper quadrant; no abnormality otherwise. Bruises are avoided as far as possible to absolve effects of confounding;
Deep palpation yields no masses, except for the enlarged liver (or the mass located over the normal anatomical location of the liver);
There is no abdominal guarding.
Liver Examination:
Gross Hepatomegaly, where the liver edge is palpated 5 centimetres below the right costal margin;
The liver edge is firm, but not tender;
Murphy's sign is negative.
The liver span, as measured down the mid-clavicular line, is greater than 12 centimetres (forgot the exact figure).
Spleen Examination:
Splenomegaly present, where the Castell Sign is positive;
It is firm in consistency.
The Castell Sign indicates the presence of splenomegaly. The spleen is usually located between the ninth and eleventh ribs. At full expiration, the percussion note over the intersection between the anterior axillary line and the left costal margin is resonant. This is due to the presence of an air-filled stomach (presumably, provided that there are no associated gastric pathologies such as outlet obstruction). Then, as the patient starts breathing in, up to the point of full inspiration, the percussion notes goes from resonant to dull, meaning that the pressure exerted on the abdomen is sufficient to render the enlarged spleen placed under the radar.
Associated Structures:
The kidneys are normal (cannot be ballotted);
The urinary bladder is not detected in the abdomen.
The abdominal aorta is normal.
The patient has mild to moderate ascites, as according to the shifting dullness test.
Auscultation: There is no hepatic bruit. Abdominal / bowel sounds are normal. No other bruits are present.
Analysis:
At this stage, we are naturally drawn to liver pathologies where the patient might be, very likely, transferred to this ward since she is waiting for liver transplantation. What interests me is the dehiscence between the severity of hepatomegaly and the variety of liver-related signs detected. There is gross hepatomegaly but many liver-related signs are absent.
This diagram shows how a living donor's liver is broken up for transplantation. It has to be noted that the liver is a magical organ and commands such homogeneity in histology that allows the magical process of regeneration. Translating this into clinical practice, it means that only part of the liver is required to be transplanted (as little as 1/4 of a full-blown liver). In time, the transplanted liver grows to the dimensions expected of a normal liver. This diagram is extracted from Cleveland Clinic.
Unearthing the actual pathology is crucial for prognostic purposes and monitoring. For instance, a patient receiving liver transplantation due to autoimmune hepatitis has an overall survival rate of 63 per cent, as compared to 53 per cent in those having done so due to a Hepatitis B-related infection. [6] As a starting point, there are several branches of causes leading to chronic liver disease. We can eliminate them one by one and rearrange them in our list of differential diagnoses by priority.
Infections related to Hepatitis Viruses (especially Hepatitis B and Hepatitis C) - This remains the one with the biggest suspicion. The patient was born and bred in China, a country of high burden of Hepatitis B, where the prevalence is higher than 5 per cent per Lancet statistics. [7] Her mother also developed Hepatitis B and is currently taking entecavir to control the disease. Although her father developed a liver condition from alcoholism, the effects of Hepatitis B could not be ruled out. Besides, Hepatitis B could be transmitted through sexual activity. There is also vertical transmission of disease. All of this means that Hepatitis B from the mother could have been transmitted inevitably to the father (depending on the use of protection) and the patient (in the womb or during delivery). There is no evidence that the patient might have Hepatitis C, or any other hepatitis viral infection. After all, the prevalence of Hepatitis C in China is below 1 per cent. [8]
Infections related to non-Hepatitis Viruses - the clinical history does not suggest anything related to acute infections and there is no evidence from the clinical history supporting that the patient might have an infection induced by EBV, HSV, Ebola or anything that has a predisposition to cause liver disease. The patient does not have immunodeficiency (like history of HIV infection) or primary/post-primary tuberculosis. Having these two might increase the risk of contracting miliary tuberculosis in the liver and fungal infections.
Fatty Liver progressing into Non-alcoholic Steatohepatitis - it does not seem to be likely. The patient's BMI is within the normal range. The patient does not have any metabolic syndrome. The patient's dietary history is unremarkable, meaning that there is no overtly significant fat consumption. The patient is a non-drinker (alcohol is a source of fat) and also exercises regularly.
Alcoholic Liver Disease - The patient has never consumed alcohol, taking the patient's word for the info. It is therefore excluded.
Metabolic (such as glycogen storage disorders) - There is no metabolic issue derived from the clinical history. Patients with glycogen storage disorders can present with stunted growth and have problems in gaining weight. I've once seen an 18-year old patient with a glycogen storage disease who looks nine years old.
Aflatoxin (hepatocellular carcinoma) - usually present in China, Southeast Asia and Sub-saharan Africa, where there is relatively high prevalence of Hepatitis B in the community and uncontrolled aflatoxin exposure [9]. These regions account for 80 per cent of the entire global burden of aflatoxin-induced hepatocellular carcinoma. Moreover, the major epidemiological burden comes from aflatoxin-laced foodstuffs. [10] Seeing that the patient, although born and bred in China, has stayed in the UK for the past three years, aflatoxin exposure is very remote as an aetiology.
Congenital (separate from metabolic disorders) - the major suspicion here is polycystic liver disease. It remains a possibility which can only be confirmed upon imaging. However, this is less likely since she does not have relevant family history of the condition (from the obtained clinical history).
Biliary Disorders & Autoimmunity - no evidence suggesting any prior biliary disorder. We are especially concerned with primary biliary cholangitis, primary sclerosing cholangitis and gallstones. The first two are not likely, where the patient is not likely to harbour predisposition to autoimmunity, since her asthma is under control and she does not have any known drug allergies, or any history of other autoimmune conditions. She also does not have relevant family history of high autoimmune tendencies.
Drug-induced - Not likely, since the patient is not undertaking any form of treatment. There is also no recreational drug use (never question the patient until the moment when the suspicion is too high).
[11] The diagram shows the typical course of alcoholic liver disease.
I also want to make some comments regarding the clinical manifestations of this patient, and chronic liver disease in general.
Bruising is a common issue amongst the general population. However, it is not common to have bruises over the trunk, or any regions which do not involve movement. These regions are usually less susceptible to trauma and are less likely to be bruised, unless there are instances of domestic abuse (that's why I brought up that point earlier). In the context of liver disease, bruising can indicate impaired liver function. The liver is responsible for producing factors of coagulation such as Factors II, V, X and von Willebrand Factor. Once it can't do its job properly, signs of hypocoagubility emerge.
Moreover, the epigastric symptoms can be attributed to the compression of the stomach by the enlarged liver. There is no suggestion of a separate condition regarding the stomach, such as peptic ulcer disease. Besides, the patient has no sign of melaena, haematemesis or pain originated from (or occurring first at) the left upper quadrant or the epigastrium. Many are confused but functional dyspepsia is an example of medics giving a name to symptoms that cannot be explained by contemporary medical science (just like the now-defunct dysfunctional uterine bleeding) and is a diagnosis by exclusion.
Not being mean, but a colleague of mine once thought the pruritus was associated with clinical examination. 'That itch must come from our examining her.' With all due respect, that statement is flawed. There is a basis for pruritus coming from hepatic disorders. This originates from biliary obstruction, Cholestasis, meaning that bile remains in one palce rather than follows, leads to the inadvertent retention of waste substances including urea. This is conducive to aberrant neural stimulation (especially regarding the serotonergic pathways), such as itchiness. There is nothing got to do with skin follicles or superficial irritation. Everything comes internally. Drugs such as sertraline and rifampicin are found to work. [12] Pruritus can also be observed in patients with renal disorders, which are, by the way, possible to be originated from a predisposing hepatic condition, such as hepatorenal syndrome in cirrhosis. [13]
Portal hypertension entails internal haemorrhoids, oesophageal varices, Budd-Chiari Syndrome, caput medusa, splenomegaly and ascites. In this patient, only the last two are observed. Budd-Chiari Syndrome is a rare hepatic entity, occurring in 1 out of 100,000 in the world. It is a disease involving hepatic venous obstruction, which leads to the accumulation of portal venous blood within the liver. There is increased intravascular pressure, leading to greater extent and rate of filtration. The increase in interstitial fluid within the liver is not corresponded by lymphatic removal. Fluid pressure continues to build in the liver. Pressure compresses against the hepatic sinusoids (which are vascular structures at the confluence of the hepatic arteriole and portal venous branch). Less blood exits the liver. Hepatocytes are injured and can undergo apoptosis Budd-Chiari Syndrome's manifestations can be summarised by the triad of right (a) upper quadrant pain, (b) ascites, and (c) hepatomegaly. [14] A causal relationship between Budd-Chiari Syndrome and portal hypertension simply cannot be established since one can be explained as the cause either way. Portal hypertension leads to vascular congestion due to decreased vascular pressure gradient across the portal circulation. This leads to stunted vascular flow and once stasis takes preponderance, there is greater chance of thrombosis. The thrombosis, as explored in my article on stroke, can easily lead to venous occlusion - i.e. Budd-Chiari Syndrome. At the same time, as mentioned above, Budd-Chiari Syndrome leads to excessive fluid retention and compression against the vascular sinusoids, leading to portal hypertension. With these competing theories in mind, they form a vicious loop.
A diagram showing the major veins draining out of the liver. The diagram is extracted from: https://abdominalkey.com/wp-content/uploads/2016/10/A304811_1_En_2_Fig6_HTML.jpg.
Investigations Ordered:
With reference to the patient's condition, i would say these investigations are more aptly known as tests used to monitor the patient's general health status. We have to see if the patient's condition has deteriorated in any way and whether any change in clinical course contributes to changes in suitability in receiving liver transplantation.
I include in the following, a scan comparable to the CT Abdomen of the patient's liver (with contrast added) to illustrate what the patient has. However, there is one difference - there is no renal involvement in this patient.
As additional details, the patient's liver function tests indicate a mixed picture - meaning that there is both biliary obstruction (high ALP and GGT) and deranged liver function (DeRitis Ratio = AST/ALT > 2.0). The patient also experiences high serum bilirubin, creatinine and urea. There is prolonged prothrombin time, indicating impaired coagulation traceable to derangement in liver function. There is no anaemia, nor leucocytosis.
From the serological results, the patient also has no active Hepatitis B. There are Anti-Hbs and Anti-Hbc IgG (long-term) antibodies, and no HBsAg - the surface antigen of Hepatitis B Virus indicative of acute infection. There is also no detectable HCV (Hepatitis C Virus) RNA through PCR.
CT Abdomen (with contrast) showing multiple cysts scattered across the hepatic and renal parenchyma. The distribution is more diffuse in the left kidney than the right kidney. There is no splenomegaly (from this image, would like to refer to other images in the stack to confirm). There is also mild ascites (the hypodense fluid collection under the abdominal skin. Polycystic kidney disease with liver cysts is the most likely diagnosis for this patient. The scan is extracted from: https://ctisus.com/resources/library/teaching-files/kidney/248778.jpg.
Pathological specimen of a polycystic liver. The picture is extracted from: https://basicmedicalkey.com/wp-content/uploads/2017/04/image01595.jpeg.
The patient is therefore most likely to have polycystic liver disease which leads to the aforementioned clinical manifestations. There is no actual hepatic disorder at first, where in most cases, patients are asymptomatic. However, as time passes, the cysts become more dominant, large and diffuse. This leads to biliary obstruction, cholestasis and hepatocyte injury. It becomes a form of chronic liver disease.
The condition should be distinguished from polycystic kidney disease with liver cysts, since polycystic liver disease does not often have renal involvement. While in 80 per cent of cases, no specific genetic mutation can be identified as the key cause, the mutation of a gene called PRKCSH is found to be significantly correlated. [15] Liver transplantation remains the only form of curative treatment.
Concluding Remarks:
This is the closest I can think of an organ placed under bubble-wrap film. It is the only time I've seen polycystic liver disease and I count myself lucky. The liver transplantation ward is a magical place and I'm learning new things every day.
*Cover picture: all credits to the Awkward Yeti; this is the exact passive-aggressiveness I expect from the liver after getting extremely smashed the night before with my dazzling beau (aka my bed).
**Lucinda Jane is a fake name given to an actual patient with the condition. Of course, since it is impossible for me to gain individual patient consent, the actual case is rendered much more fictional than factual. Patient particulars are entirely removed and many details are altered to exaggerate the things I want to say. This includes the patient's heritage and family history.
References and Further Reading:
[1] Chandok N. Polycystic liver disease: a clinical review. Ann Hepatol. 2012;11(6):819-826. doi:10.1016/s1665-2681(19)31406-1.
[2] Suwabe T, Chamberlain A, Killian J et al. Epidemiology of autosomal-dominant polycystic liver disease in Olmsted county. JHEP Reports. 2020;2(6):100166. doi:10.1016/j.jhepr.2020.100166.
[3] Aussilhou B, Dokmak S, Dondero F et al. Treatment of polycystic liver disease. Update on the management. J Visc Surg. 2018;155(6):471-481. doi:10.1016/j.jviscsurg.2018.07.004.
[4] Spleen Exam. Stanford Medicine 25. https://stanfordmedicine25.stanford.edu/the25/spleen.html. Published 2020. Accessed December 20, 2020.
[5] Liver Exam. Stanford Medicine 25. https://stanfordmedicine25.stanford.edu/the25/liver.html. Published 2020. Accessed December 20, 2020.
[6] Stravitz RT, Lee WM. Acute liver failure. Lancet 2019;394:869-81.
[7] Schweitzer, A., Horn, J., Mikolajczyk, R. T., Krause, G. & Ott, J. J. 2015. Estimations of worldwide prevalence of chronic hepatitis B virus infection: a systematic review of data published between 1965 and 2013. Lancet, 386, 1546-55. 17 Oct 2015.
[8] The CDA Foundation. Hepatitis C country profiles. Lafayette, CO: CDA Foundation, 2017. Available from http://polarisobservatory.org/. Accessed on 30 October 2017.
[9] Liu Y, Wu F. Global burden of aflatoxin-induced hepatocellular carcinoma: a risk assessment. Environ Health Perspect. 2010;118(6):818-824. doi:10.1289/ehp.0901388.
[10] Hamid AS, Tesfamariam IG, Zhang Y, Zhang ZG. Aflatoxin B1-induced hepatocellular carcinoma in developing countries: Geographical distribution, mechanism of action and prevention. Oncol Lett. 2013;5(4):1087-1092. doi:10.3892/ol.2013.1169.
[11] Simonetto D, Shah V, Kamath P. Outpatient management of alcohol-related liver disease. The Lancet Gastroenterology & Hepatology. 2020;5(5):485-493. doi:10.1016/s2468-1253(19)30415-7.
[12] Mayo M, Handem I, Saldana S, Jacobe H, Getachew Y, Rush A. Sertraline as a first-line treatment for cholestatic pruritus. Hepatology. 2007;45(3):666-674. doi:10.1002/hep.21553.
[13] Low G, Alexander GJ, Lomas DJ. Hepatorenal syndrome: aetiology, diagnosis, and treatment. Gastroenterol Res Pract. 2015;2015:207012. doi:10.1155/2015/207012.
[14] Aydinli M, Bayraktar Y. Budd-Chiari syndrome: etiology, pathogenesis and diagnosis. World J Gastroenterol. 2007;13(19):2693-2696. doi:10.3748/wjg.v13.i19.2693.
[15] Li A, Davila S, Furu L, Qian Q, Tian X, Kamath PS, King BF, Torres VE, Somlo S. Mutations in PRKCSH cause isolated autosomal dominant polycystic liver disease. The American Journal of Human Genetics. 2003;1;72(3):691-703.