Carbonic
Anhydrase
II Deficiency
Syndrome:
Recessive
Osteopetrosis
With
Renal
Tubular
Acidosis
and Cerebral
Calcification
Arne Ohlsson, MD, FRCP(C), William A. Cumming, MD, FRCP(C),
Adrien Paul, MD, FRCP(C), and William S. Sly, MD
From the Division of Neonatology, Departments of Pediatrics and Radiology, King Faisal Specialist Hospital and Research Center, Riyadh, and Department of Pediatrics, King Khalid Military City Hospital and Health Services, Hafar Al Batan, Saudi Arabia; and E. A. Doisy Department of Biochemistry, St Louis University School of Medicine,
St Louis, Missouri
ABSTRACT. Four new Saudi Arabian cases of the
car-bonic anhydrase II deficiency syndrome from two families are described. This autosomal recessive syndrome
in-cludes osteopetrosis with renal tubular acidosis and
cer-ebral calcification. Additional features are mental
retar-dation, growth failure, typical facial appearance, and
abnormal teeth. Two patients showed evidence of restric-tive lung disease, a finding not previously described. One
of the patients reported represents the first neonate reported to be affected with this syndrome. Intrauterine growth was normal, but metabolic acidosis was already
evident in the neonatal period. Radiographic evidence of
osteopetrosis was probably absent at birth but appeared
during the late neonatal period. Carbonic anhydrase II deficiency was demonstrated in erythrocyte hemolysates
from the older two siblings of this neonate, and a 50%
normal level of carbonic anhydrase II was demonstrated
in the erythrocyte hemolysate from their father. Pediat-rics 1986;77:371-381; carbonic anhydrase II, osteopetrosis, renal tubular acidosis, intracranial cakification, infant, neonate.
The association of osteopetrosis and renal tubu-lar acidosis was first noted in three different
fami-lies in 1972.13 In 1980, Ohlsson et al.4 described, in four children from three Saudi Arabian families, a syndrome that consisted of osteopetrosis, renal
tu-bular acidosis, and the new finding of cerebral calcifications, for which the authors proposed the
Received for publication April 8, 1984; accepted June 19, 1985. Reprint requests to (A.O.) University ofToronto Perinatal Com-plex, Regional Perinatal Unit, Women’s College Hospital, 76 Grenville St, Toronto, Ontario, Canada M5S 1B2.
PEDIATRICS (ISSN 0031 4005). Copyright © 1986 by the American Academy of Pediatrics.
name “marble brain disease.” The syndrome was
clinically associated with mental retardation, stunted growth, abnormal teeth, and special facial features. The syndrome was inherited as an auto-somal recessive trait. The same year, Whyte et al5
independently reported intracranial calcifications
in the American sibship with osteopetrosis and
renal tubular acidosis that originally had been
re-ported in 1972 by Sly et al.#{176}In 1983, Sly et al
identified carbonic anhydrase II deficiency in
eryth-rocytes of patients from the same American family and proposed that carbonic anhydrase II deficiency was the primary defect in this syndrome.6 These findings were later extended to many other families with this syndrome, including several families from Saudi Arabia.7 In the same year, Venta et a18 located the gene for carbonic anhydrase II to chromosome number 8.
In this report, we describe clinical, radiologic,
and biochemical findings in four additional patients with this disorder including the first neonate, and we review the literature regarding this now
well-defined syndrome of which 17 cases have been
previously reported in detail.#{176}#{176}’912
CASE REPORTS
Developmental data and physical measurements are
summarized in Table 1, and the important biochemical
data are shown in Tables 2 and 3. All infants had normal
serum creatinine and sodium levels. Ammonium chloride
acidification test (0.1 g of ammonium chloride per kilo-gram of body weight, orally) was performed in cases 2
and 3. Carbonic anhydrase II was analyzed in blood
Case
No.SexAge (yr)Height Age (yr)Bone
Age
Greulich-PyleDevelopmentalLevel
(yr)(yr)1M21@/121@/120@/i22M115%256/124@/123M836/1236/124@/u24MNewbornNewbornNewbornNormal
TABLE 2. Biochemical
DataTestCase
1: 1983
April AprilJuneCase
2: 1984Case 3: 1984Case
4:FebMarchMarch
MarchAprilMayMarchMarch AprilMayJune4
27727711 28*417*1128*
417@13SerumBUN
(mg/dL)16.8 13.099 813141521
161613Ca
(mg/dL)10.69.48.58.7 9.48.99.29.110.4 9.99.89.8K
(mmol/L)3.3 5.03.43.73.9 3.73.74.13.94.2 4.03.93.9Cl
(mmol/L)107 119110106108 110106110115115 113111114Total
CO2 (mmol/13.6 9.321.922.025.0 22.023.016.021.018.0 20.015.09.0L)Uric
acid (mg/dL)3.23.44.74.3 4.95.65.23.23.3 3.63.74.3P
(mg/dL)5.82 3.666.35.95.4 5.66.56.05.56.8 6.55.26.0LDH
(U/L)576503
435295685436493
628474652Phosphatase
(U/L):Alkaline105100
107100126144127 141132395Acid2.652.55Zn
(@g/dL)t10597Parathyroid
hor 58.563.8mone (pmol/L)@Blood:
Hgb
(g/dL)9.912.012.09.29.910.911.911.611.216.5PlasmaRenin@
(ng/mL/h)6.3 0.99.11.6Aldosteronell
(ng/12.7 4.339.08.7dL)l.25(OH)2
vitamin59.069.0D3
(ng/mL)1lUrine:
Specific gray1.0201.0221.0301.0221.006ity
optic atrophy
with light perception
the best probable
vision. No other neurologic abnormality was found.
Investigations.
Radiographic
skeletal
survey showed
generalized osteopetrosis (Fig 1), but intracranial calci
fications were not seen on skull films. A barium enema
of the colon demonstrated generalized dilation, marked
atonicity,
and poor evacuation.
Computed tomography
(CT) of the brain was not performed. There was evidence
of iron deficiency anemia and renal tubular acidosis but
no biochemical findings of rickets. Serum calcitonin was
10 pg/mL (reference value, males 2 to 17 pg/mL). His
karyotype was that of a normal male, 46,XY. Findings
on routine urinalysis and calcium excretion in a 24-hour
urine specimen were normal.
Case2
This Saudi boy was first seen at 10 years of age for an
abscess following tooth extraction 9 months earlier. Par
ents were not closely related but belonged to the same
tribe. The father was 46 years old and the mother 31
years old. Two younger brothers (patients 3 and 4) were
similarly affected. Two sisters, 9 and 2 years old, were
healthy; one sister had died at the age of 1 month. The
father was also married
to another
woman who was
gravida 9, para 9, involving one stillbirth,
one neonatal
death, and seven healthy living children. The patient's
mother's pregnancy and delivery were normal. The pa
tient sat at 6 months of age and walked at 12 months; he
Case1
A Saudi boy was first seen at 2 years of age for
developmental delay and chronic constipation. Parents
were first cousins; there were no siblings. The patient's
mother's
pregnancy
and delivery were normal, but the
patient's psychomotor development was delayed. He was
unable to sit or stand or to speak a single word at 2 years
of age. He had had no known fractures.
Examination.
Findings from the physical examination
were: height 80 cm, weight 8.1 kg, occipital frontal cir
cumference 47.5 cm, unusual facial appearance with rel
atively large skull in comparison with the face, abnormal
teeth with enamel hypoplasia and malocclusion, and nor
ma! hand creases. No hepatosplenomegaly was found, but
large amounts of feces were palpated on abdominal ex
amination and fecaloma was found on rectal examination.
Other findings were normal male genitalia, normal hear
ing, esotropia with nonfixation of either eye, and bilateral
TABLE 1. GrowthandDevelopment
* On treatment with NaHCO3.
t Normal value 70 to 120 @ug/dL.
:1:
Normalvalue29to 85pmol/L.
§
Normalvalue7 to 9 years,2.13±0.44ng/mL/h;10to 11years,1.96±0.36.
IINormal
value7to 11years,
5to70ng/dL.
TABLE 3. Acid-Base Status
Case No.
Date Arte rial Blood
pH Urine
Pco2
pH Pco2 HCO3 Base
(mm Hg) (mmol/L) Excess (mm Hg)
(mmol/L) 1 4/5/83 5/10/83 7.17 7.26 11.4 19.3 15.2 6.9 6.0 7.0 2 2/27/84 3/7/84 3/10/84 3/11/84 3/12/84 3/20/84* 3/28/84* 4/4/54* 4/8/84* 5/16/Mt 7.29 7.35 7.32 7.38 7.31 7.44 7.45 7.30 7.40 7.31 39.4 31.8 34.8 35.4 41.1 35.1 30.0 47.0 29.2 40.0 19.0 17.6 18.0 20.8 20.9 23.7 21.0 23.0 17.8 20.0 7.7 6.6 6.9 3.0 4.6 0.5 1.6 0.3 5.4 5.4 6.0 6.0 7.1 7.2 7.6 7.6 104.4 3 4 3/11/84 3/12/84 3/20/84* 3/28/84* 4/4/54* 4/8/84 5/16/84 6/13/84 7.34 7.25 7.36 7.33 7.29 7.38 7.39 34.1 37.0 43.5 30.6 42.0 33.3 29.0 18.2 16.0 24.6 16.2 20.0 19.7 18.0 6.2 10.0 0.3 8.1 6.0 4.0 6.0 6.6 7.3 7.7 6.8 69.3
* On oral treatment withNaHCO3, 5 mEqjkg/d.
t Treatment discontinued for eight hours.
:1:On oral treatment with NaHCO3, 6 mEqJkg/d.
TABLE 4. Tests*
Carbonic Anhydrase (CA) II Deficiency
Subject Starch Im- High CA II
Gel muno- Pressure CO2
Electro- diffusion Liquid Hydratase phoresis Anti-CA Chroma- (U/mg
II tography hemoglobin)
(CA 1/ CA II)
Patient 2 0 0 >iO 0
Patient 3 0 0 >i0 0
Father (+) + 27 3.7
Control + + 5.1 9.7
* Starch gel electrophoresis, immunodiffusion, and re-verse-phase high pressure liquid chromatography were performed as previously described.6 CO2 hydratase activ-ity (units per milligram of hemoglobin) was measured as
described by Maren and Couto’3 following incubation of
the enzyme in 20 mmol/L brompyruvic acid at pH 6.8 for two hours at 25#{176}.This treatment selectively inactivates
CA I and allows measurement of CO2 hydratase activity exclusively due to CA II. Patients 2 and 3 were CA II deficient by all criteria, and their father was scored as a
heterozygous carrier for CA II deficiency. +, CA II activ-ity present; (+), CA II activity present but decreased compared with control.
seemed to grow in a normal way until age 2 years when
his physical and psychomotor development was noted to
be slow. He had started school at 9 years of age but could not manage and left after 1 week. He had fractured his
left leg at 8 and at 10 years of age.
Examination. His height was 110 cm, weight 18.7 kg, and occipital frontal circumference 46 cm. He had an
unusual facial appearance with a relatively large skull,
small lower jaw, abnormal teeth with several teeth
miss-ing, enamel hypoplasia, caries, a right-sided maxillary
oral-antral fistula, with purulent drainage into the mouth and from the right nostril, and swelling of that part of
the face (Figs 2 and 3). Other findings were mild chest
deformity (Fig 2), normal hand creases, no
hepatosple-nomegaly, normal male genitalia, genu valgum, abnormal
modeling of proximal tibiae (Fig 2), nystagmus, bilateral optic atrophy, and near normal vision. Audiogram
find-ings demonstrated hearing thresholds within normal
lim-its but a slight conductive hearing loss.
Investigations. A radiographic skeletal survey showed generalized osteopetrosis and a healing fracture of the
distal left tibia. Many of the bones had a “bone within a bone” appearance. The optic foramina were of normal size. Lung roentgenograms showed no parenchymal
dis-ease but dense ribs.
CT showed normal kidneys with no nephrocalcinosis.
Intracranial calcifications, visible on skull films, were shown by CT to be in the basal ganglia. There were other calcifications in the frontal and occipital lobes, close to the junction between gray and white matter (Fig 4). Electroencephalogram (EEG) findings were abnormal for
the patient’s age and showed slow background activity. Pulmonary function test findings demonstrated moderate
to severe restrictive lung disease with vital capacity 51%
and total lung capacity 57% of predicted capacity. The
child underwent a Caldwell-Luc procedure, and a bone specimen was obtained during the operation that revealed
chronic osteomyelitis; but the specimen was not adequate for further microscopic studies. Culture of the bone grew
Hepa-Fig 1. Case 1.Osteopetrosis, clubbing,and horizontal
banding of femora.
Fig 2. General appearance at 11 years (left, patient 2),
at 8 years (middle, patient 3), and their normal sister (right) at 2 years of age.
rinized blood samples from case 2, case 3, their father, and a normal control subject were shipped on wet ice by air carrier to the United States, where erythrocyte hem-olysates were prepared as described previously6 and
as-sayed for carbonic anhydrase levels by several methods.
These results, presented in Table 4, document the defi-ciency of carbonic anhydrase II in the two affected pa-tients and the reduced levels of carbonic anhydrase II in
their father. As in all prior cases of this syndrome examined7 no carbonic anhydrase II was detectable in
erythrocyte hemolysates of affected patients, and car-bonic anhydrase I levels appeared normal. Other studies showed renal tubular acidosis but no biochemical
evi-dence of rickets. An ammonium chloride acidification test demonstrated bicarbonate in the urine with a pH of 6.3 to 7.2 and reduced net acid secretion in spite of a pH of 7.31 and bicarbonate of 20.9 mmol/L in arterial blood.
The titratable acid level on 24-hour urine collection was 5.5 tEqJmin/m3 (normal = 2.0 to 29.2 MEqJmin/m3),
whereas the serum bicarbonate ranged from 18 to 20.8 mmol/L and the urine pH was 6.7. Results of routine urinalysis and amino acid screen in urine were normal. Creatinine clearance was 90 mL/min/1.73 m2 and tubular
reabsorption of phosphate 85%. Calcium excretion in
urine was 2.25 mg/kg/24 h, chloride 147 mEqj24 h, potassium 3 mEqj24 h, and sodium 60 mEqJ24 h. Serum
iron was 31 ug/dL (normal 42 to 135 ag/dL), and total iron binding capacity was 246 xg/dL (normal = 280 to
400 xg/dL). Smears of peripheral blood revealed
micro-cytic hypochromic anemia. The karyotype was that of a normal male, 46,XY.
Case 3
A Saudi boy, first seen at 8 years of age because of retarded growth and development, was the brother of patients 2 and 4. Born after a normal pregnancy and delivery, he sat at 6 months of age and walked at 12 months. He started school at 6 years of age but was noted to be slow and could not “fight for himself” and left school. No history of fractures was reported.
Examination. Findings on physical examination were height 99 cm, weight 15 kg, occipital frontal
circumfer-ence 50 cm, prominent forehead with triangular face and small lower jaw, abnormal peg-shaped teeth with enamel
hypoplasia and caries (Fig 2), normal hand creases, no
hepatosplenomegaly, normal genitalia, and genu valgum. Findings on eye examination were of normal vision but
very mild optic atrophy. Audiogram results demonstrated mild conductive hearing loss. He had an abnormal EEG, exhibiting background slowing for patient’s age.
Radio-graphic skeletal survey findings were of generalized
Fig 3. Case 2. Abnormal teeth, malocclusion, peg-shaped teeth, and enamel hypoplasia.
Fig 4. Case 2. Computed tomographic scan showing symmetrical calcification of basal ganglia and
calcifica-tion in frontal and occipital lobes close to junction
be-tween gray and white matter.
A chest radiograph showed dense bones and normal lungs. Optic foramina were normal. Brain CT showed dense
symmetrical calcification in the basal ganglia, particu-larly in the caudate nuclei and the putamen. CT showed normal kidneys with no nephrocalcinosis. Pulmonary function study results indicated a restrictive process with total lung capacity 44% of predicted, vital capacity 50% of predicted, and residual volume 174% of predicted.
There was no biochemical evidence of rickets. Ammo-nium chloride acidification test resulted in appropriate net acid secretion, no bicarbonate in the urine, urine pH
6.0 at a pH of 7.25 and bicarbonate of 16 mmol/L in
arterial blood. Results of routine urinalysis and amino
acid screen in urine were normal. Creatinine clearance
was 59 mL/min/1.73 m2. Tubular reabsorption of
phos-phate was 86%. Urine excretion of calcium was 2.6 mgI
kg/d, potassium 35 mEqJ24 h, sodium 53 mEqj24 h, and
chloride 57 mEqJ24 h. His karyotype was that ofa normal male, 46,XY.
Case 4
A Saudi boy first seen at 23 days of age was the brother
of the patients 2 and 3. Antenatal ultrasonographic
ex-amination of the fetus at 34 weeks’ gestation revealed appropriate growth for gestational age, no abnormalities, and normal amount of amniotic fluid. He was born after a normal pregnancy and normal delivery at term. He cried immediately, and the early neonatal period was
normal. At 23 days of age, he was taking breast milk but was supplemented with formula. He was having loose
stools but no other complaints. He did not smile but could fix his eyes on his mother.
Examination. Findings on physical examination were length 50.5 cm, weight 3.72 kg, occipital frontal circum-ference 36 cm, eyelids and eyebrows painted with kohl, prominent forehead and small lower jaw, and normal
hand creases (Fig 5). His breathing pattern and chest
were normal, there was no hepatosplenomegaly and he had normal male genitalia. He could fix light, and his
pupils reacted normally to light; fundi were normal. He
responded to sound. He had normal Moro, grasp, and
sucking reflexes, and his development was normal for his age. Radiographic skeletal survey results were normal
pha-Fig 5. Case 4. Facial appearance at 23 days of age.
DISCUSSION
langes and fifth digit clinodactyly with middle phalangeal
hypoplasia (Fig 6). Laboratory investigations showed no
anemia but hyperchloremic metabolic acidosis and
alka-line urine compatible with renal tubular acidosis. Stool
culture was negative for bacterial growth.
Treatment
Patients 1, 2, and 3 were given 5 to 6 mEq of sodium bicarbonate per kilogram of body weight
per 24 hours orally. An increase in arterial blood pH and bicarbonate levels reversed quickly when the supplement was stopped. No significant change
was recorded in serum chloride, potassium, or so-dium values on treatment with NaHCO3, but there was a significant decrease in plasma renin and aldosterone levels in patients 2 and 3 (Table 2).
Iron deficiency anemia in patients 1 and 2
re-sponded to treatment with iron. Patient 2 had osteomyelitis of the right jaw that improved after a Caldwell-Luc procedure and treatment with anti-biotics. Patient 1 has been lost to follow-up, and the observation time is too short in patients 2 and
3 to know whether treatment with NaHCO3 will affect growth.
The four children described are suffering from a
syndrome that includes osteopetrosis, renal tubular acidosis, characteristic facial appearance, severe
re-tardation of growth and development, and cerebral calcification as described independently by Ohlsson
et al4 and Whyte et al5 in 1980. The patients de-scribed by Whyte et al differ in that their mental development was less affected.5
The lack of carbonic anhydrase II activity in
patients 2 and 3, and 50% activity of carbonic anhydrase II in the father, is consistent with find-ings in several other families, implicating carbonic anhydrase II deficiency as the primary defect in
this syndrome.#{176}’7 All of the clinical manifestations,
which will be discussed in detail, can presumably
be explained by the deficiency of carbonic anhy-drase II, a water-soluble zinc metalloenzyme that catalyzes the reversible hydration of CO2. The en-zyme is distributed in many different tissues
in-cluding RBCs, bone, glial tissue, lungs, and proxi-mal and distal renal tubules.
The main characteristics of these four new cases are summarized in Table 5 together with available data for the 17 previously reported patients with
some or all features of this syndrome.
TABLE 5. Osteopetrosis Associated With Renal Tubular Acidosis and/or Intracerebral Calcifications: Reported Cases*
Summary of
Case No.
Age (yr)
Sex Parents Related
No. of Affected Siblings/
Osteo-petrosis
Renal Tubular Acidosis
Intra-Cerebral Calcification
Short Stature
Mentally Retarded
Reference No.
Total Siblings
1 2 M + 0/0 + + + + +
2 11 M t 2/4 + + + + +
3 8 M t 2/4 + + + + +
4 </12 M t 2/4 + + - -
-5 8/12 M
+ 1/3 + + - + + 4
6 38/12 F
+ 1/3 + + + + + 4
7 5/12 M + 1/8 + + + + + 4
8 7 F + 0/2 + + + + + 4
9 4 M + 0/2 + + ? + - 2
10 1’%2 M + 1/4 + + ? + 1
11 6/12 M + 1/4 + + ? + 1
12 22 F - 2/3 + + ? + (+) 3
29 + 5,6
13 17 F - 2/3 + + ? + (+) 3
24 + 5,6
14 15 F - 2/3 + + ? + (+) 3
22 + 5,6
15 15 M t 1/5 + + + + + 9
16 10 F t 1/5 + + - + + 9
17 35 M + 2/8 + ? + + + 10
18 45 M + 2/8 + ? + + + 10
19 25 F + 2/8 + ? + + + 10
20 4#{189} F + 0/0 + + - - + 11
21 /12 M ? ? + + ? ? ? 12
* + indicates “yes” or “present”; (+) indicates intelligence in the low normal range;
questionable.
t Same tribe.
:1:Transient motor retardation.
- indicates “no” or “absent”; ?,
IMPLICATIONS
Inheritance
These case reports provide additional evidence for autosomal recessive inheritance of this
syn-drome. The healthy parents of patient 1 are first cousins, and the unaffected parents of patients 2, 3, and 4 belong to the same Saudi tribe in which
intermarriage is the rule. The father of patients 2,
3, and 4 was an obligate carrier for the disease and
showed a 50% decrease in activity of carbonic
an-hydrase II in his RBCs. His marriage to a different
spouse, presumably a noncarrier, produced no af-fected children in nine pregnancies. The literature review also provides compelling evidence for
auto-somal recessive inheritance; there are reports of
frequently related healthy parents and sibships with multiply affected and unaffected siblings of both sexes.17’9’2
Osteopetrosis
Osteopetrosis, first described by Albers-Sch#{246}n-berg in 1904,’4has been considered to occur
predom-inantly in two forms: a malignant (lethal,
congeni-tal) autosomal recessive type and benign (adult, tarda) autosomal dominant type.1517 However, in-termediate autosomal recessive forms without a
malignant course have also been reported.#{176}2#{176}The
malignant recessive form is seen in early infancy
with anemia, hepatosplenomegaly, failure to thrive,
and cranial nerve symptoms.’7 The benign form may go undetected for many years, although the abnormal bones fracture easily.15
The skeletal radiologic findings in these new
patients are indistinguishable from previously
de-scribed forms of osteopetrosis’47 and identical with
those in previous reports of this syndrome in
chil-dren.”2’4’9 Increased bone density, abnormal
mod-eling, transverse banding of metaphyses, fractures,
and “bone in bone” appearance are present.
No well-documented case of osteopetrosis in a fetus or a newborn infant has been reported.’6 The
roentgenographic findings in our neonate were very subtle, although the biochemical evidence for the disease was present at 23 days of life with severe hyperchloremic metabolic acidosis and alkaline
Apart from transient anemia in patient 1, we found no evidence of marrow failure. This has been the case previously.14’#{176} On the other hand, the ma-lignant form of osteopetrosis is usually fatal be-cause of severe anemia.’7 Carbonic anhydrase has previously been implicated in bone resorption. It has been suggested that parathyroid hormone ac-tivates carbonic anhydrase in certain bone cells, where it might aid the resorptive process by
me-diating secretion of H”.2125 The lack of carbonic anhydrase II in the siblings described by Sly et al,#{176} in subsequently examined pedigrees,7 and in pa-tients 2 and 3 in this report specifically implicates the carbonic anhydrase II isoenzyme in bone re-sorption, and its absence appears to underline the
bone abnormalities in this syndrome.
Renal Tubular Acidosis
All four patients sustained metabolic acidosis
with hyperchioremia, normal anion gap, inappro-priately alkaline urine (pH > 6.0), without signifi-cant reduction in glomerular filtration rate or ele-vation of blood urea nitrogen or serum creatinine. These findings establish the diagnosis of distal renal tubular acidosis.26’27 Other findings commonly associated with distal renal tubular acidosis such as hypocalcemia, excessive urine excretion of po-tassium, hypercalciuria, and nephrocalcinosis were lacking.26’27
The findings in patient 2 of an inappropriately alkaline urine (pH 6.3 to 7.2) and reduced net acid
excretion in spite of mild metabolic acidosis (serum
bicarbonate level 20 to 22 mEq/L) are also compat-ible with proximal renal tubular acidosis. The threshold for bicarbonate spilling in this patient
appeared to be at a serum bicarbonate level of 20
to 21 mmol/L. Similar results were found on 24-hour urine collection in patient 2, with a titratable acid value of 5.5 aEqJmin/m#{176} (normal range 2.0 to
24.2 Eq/min/m#{176}) at a serum bicarbonate level of
18 to 20.8 mmol/L. The findings on a short
acidi-fication test in patient 3, of a decrease in urine pH
to <6, of appropriate net acid excretion, and of no
bicarbonate in the urine at a serum bicarbonate
level of 16 mmol/L are also compatible with prox-imal renal tubular acidosis. Increased plasma renin
and high aldosterone levels as seen prior to treat-ment with NaHCO3 in patients 2 and 3 occur in
both proximal and distal renal tubular acidosis.26’27
Although tubule maximum bicarbonate was not
measured, these two patients show evidence of both
proximal and distal renal tubular acidosis.
Previous reports vary regarding the type of renal
tubular acidosis associated with osteopetrosis. Gui-baud et a11 found low bicarbonate thresholds but
normal distal tubular acidification. The patient
re-ported by Vainsel et a!2 had evidence of both
prox-imal and distal renal tubular acidosis. The four patients reported by Ohlsson et al4 and the three patients reported by Sly et al3 had distal renal
tubular acidosis, but an element of proximal renal tubular acidosis could not be excluded. Bourke et
a19 studied two Arab siblings with the syndrome. They found definite evidence of distal renal tubular
acidosis but could not exclude a degree of proximal
bicarbonate leak. The patient of Bregman et al1’
also had distal and proximal renal tubular acidosis.
Thus, it appears that patients with this syndrome
who are lacking carbonic anhydrase II have a
com-bination of proximal and distal renal tubular aci-dosis. Carbonic anhydrase II is the major soluble isoenzyme present in the kidney and mediates the hydration of C02, generating some of the H
se-creted by the proximal tubule.28#{176}#{176}Reclamation of bicarbonate is dependent on H secretion which can thus explain the proximal component of renal
tubular acidosis in this syndrome.#{176}3#{176}
The distal component of renal tubular acidosis is
consistent with immunohistochemical evidence for
carbonic anhydrase II in the distal tubules, where
it may either generate H or titrate OW.3#{176}The
catalytic activity and the immunoassayable amount of carbonic anhydrase II in the fetal kidney in-creases with gestational age, and many nephrons might be able to reabsorb bicarbonate and secrete hydrogen ions at 24 to 26 weeks’ gestation.#{176}4 A
newborn with the syndrome of osteopetrosis and
renal tubular acidosis would, therefore, be expected
to show hyperchloremic metabolic acidosis and im-paired urinary acidification, as was the case in our 23-day-old neonate.
Growth Failure
All children reported here except the neonate
were very short for their ages (Table 1), and three of them were also underweight. Bone age was
re-tarded and corresponded to height age. Occipital
frontal circumference was less affected. Genu val-gum is a frequent finding in this syndrome.4’5’9 Retarded growth has also been noted in the other reports of this syndrome.’5’9”#{176} Stunting of growth also occurs in malignant, recessive osteopetrosis, probably as a sequence to anemia and infection.
Acceleration of growth following correction of
aci-dosis was noted by Guibaud et al.’ In our cases,
renal tubular acidosis is the most likely cause of
the growth failure as noted previously.4 Our neonate
had grown normally in utero and had normal height and weight at 3 weeks of age. This indicates that
Facial Appearance CNS
A definite facial similarity was noted among
chil-dren suffering from this disorder by Ohlsson et al,4
and patients 1 to 4 in our present report resemble very much those previously reported (Figs 2 and 5).
Characteristically, the head is broad with promi-nent forehead, the cranial vault is relatively large in relation to the facial structures, and there is a
prominant narrow nose and slight epicanthic folds. The upper lip is relatively thin, the philtrum poorly developed and the lower lip everted in association
with micrognathia. Squint is common and
contrib-utes to the overall similar appearance of children
affected with this syndrome. A special “adenoidal” face has been noted in children with malignant
recessive osteopetrosis,17 but in the autosomal dom-inant form, the appearance is unremarkable. The
neonate in this report resembled the older brothers,
especially in the fact that the lower jaw was small.
The dentition was abnormal in our cases, with
peg-shaped lateral incisors and canines, malocclu-sion, enamel hypoplasia, and severe caries identical with the cases reported in 1980. Sly et a13 and
Whyte et a15 also noted severe dental malocclusion
in the cases reported in 1972 and 1980, respectively.
The other reports lack information on dentition. Delayed dentition and severe caries are seen both
in autosomal recessive and autosomal dominant forms of osteopetrosis. A carbonic anhydrase is
normally present in developing teeth, but the iso-enzyme has not been identified.
Lung Disease
Arterial blood gas findings in both patients 2 and
3 occasionally revealed evidence of respiratory aci-dosis with low pH and inappropriately high CO2 for
the metabolic acidosis from which these patients
suffered. These findings led us to do pulmonary function tests which demonstrated in both boys a moderate to severe restrictive lung disease. The
boys did not show any signs of respiratory distress,
and chest films showed no parenchymal lung
dis-ease but very dense rib cages. Patient 2 also had a
visible deformity of the chest.
A restrictive lung disease has not been reported
previously in this syndrome. The mechanism un-derlying the restrictive lung disease in these pa-tients is not clear.
It is possible that the total carbonic anhydrase
activity (carbonic anhydrase I and carbonic
anhy-drase II) in patients with this syndrome is border-line for CO2 delivery to circulating erythrocytes and
CO2 discharge from the lungs. In addition, the abnormal bone may cause a stiff and deformed rib cage that has a mechanical influence on ventilation.
All four of our patients were severely retarded,
as has been the case in most other reports (Table
5). With the exception of optic atrophy, strabismus, and nystagmus seen in these and previously
re-ported cases, neurologic manifestations have been
lacking. Optic atrophy in these cases was not due
to bony compression of the optic nerve, because
optic foramina were of normal size. Thus, the mech-anism of the optic nerve atrophy is not clear. CT findings in patients 2 and 3 are identical with those
reported in 1980 by Ohlsson et al.4 The
calcifica-tions are in the caudate nucleus, putamen, and globus pallidus, and peripherally in the subcortical region. They increase with age and can be seen
sometimes after the age of 18 months by CT and later on x-ray films.35 CT is more sensitive than
conventional radiography in detecting calcification. Psychomotor retardation precedes the findings of calcifications.4 No symptoms from the cerebellum have been noted. Patients 2 and 3 also had abnor-mal EEG findings with slow background activity
similar to the cases reported in 1980. Carbonic anhydrase II is primarily a glial enzyme in cerebral and cerebellar tissue and occurs predominantly in nonneuronal cells such as oligodendrocytes and in myelinated nerve fibers.3#{176}
The exact mechanism behind the formation of calcifications in the brain in this syndrome is un-known, and histochemical studies on brain tissue
have not been performed. There was no biochemical evidence of hypoparathyroidism in our cases or in
the ones reported in 1980. It is known that
para-thyroid hormone activates carbonic anhydrase in certain bone cells mediating secretion of H”2125 as carbonic anhydrase does in brain tissue. It is,
there-fore, possible that carbonic anhydrase is the
com-mon link in the calcifications of basal ganglia seen in both hypoparathyroidism#{176}7 and carbonic anhy-drase II deficiency syndrome.
Antenatal Diagnosis
Antenatal diagnosis has not been performed in
this disorder. Ultrasonography or fetoscopy are not diagnostic, but analysis of carbonic anhydrase II on fetal blood or amniotic cells might prove to be of value in this syndrome. Carriers can be detected.6’7
SUMMARY
The four patients from two families reported here suffer from a distinct autosomal recessive disease
entity. This syndrome includes osteopetrosis, renal
tubular acidosis with both proximal and distal
growth failure, typical
facial features,
and abnormal
teeth.4'5 Deficiency
of carbonic
anhydrase
II was
demonstrated
in patients
2 and
3. Activity
was
reduced to 50% of normal in their father. Similar
enzymatic
findings
have been made in all patients
with this syndrome
tested to date.7'38 The generality
of these findings
indicates
that carbonic
anhydrase
II deficiency is the underlying basis for this inborn
error of metabolism
which we now refer to as the
carbonic anhydrase
II deficiency syndrome. Devel
opment
in utero appears
to be normal,
and the
skeleton
at birth
is radiologically
normal.
Our neo
nate showed only slight sclerosis of the distal ends
of the phalanges.
However,
biochemical
evidence
of
the disease was present
in the neonatal
period.
The
facial appearance
was similar
in the neonate
to that
in older
patients.
Basal
ganglia
calcification
ap
pears
sometime
after
18 months
of age and is pre
ceded by developmental
delay. Restrictive lung dis
ease was found
in two of the patients,
suggesting
that this finding may be an additional clinical man
ifestation
of carbonic
anhydrase
II deficiency.
Car
bonic anhydrase
II deficiency should be considered
in hyperchloremic
metabolic
acidosis
in the
neo
nate. Whether
bone marrow
transplantation
could
alleviate
some
of the
manifestations
of this
syn
drome is not known. Antenatal
diagnosis is theo
retically possible.
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THE RESEARCHER’S CHILD
Our daughter Asha grew up among endless conversations of our research
work. Her first year of life unfolded between the pages of the book we edited on
Platelets, Prostaglandins and Cardiovascular Disease. Subsequently, as she grew, nighttime discussions were on platelets and prostaglandins, dinner con-versations on meetings and abstracts, bedtime stories were our manuscripts, and family albums were stacked with slides relating to our research data. Vacations were squeezed in between Mommy’s and Daddy’s presentations at various meetings. Nevertheless, Jay and I never noticed that Asha was different
from any of her school friends. Recently, however, in preparation for her seventh birthday party, I told my daughter to bring me telephone numbers of her school friends so I could call their mothers to invite them. To my surprise, Asha returned home the next day with a 12-column spread sheet. The spread sheet was neatly labeled: Invitation List for Asha Mehta’s Seventh Birthday Party. Each column was neatly sublabeled: Guest Number, Name, Date of Birth,
Address, Nationality, Mother’s Name, Father’s Name, Number of Children in Family, Telephone Number, Response of Parents, and Remarks. Each row contained complete information on each potential guest. Finally, each column was boxed off, as though ready for statistical analysis. We finally realized the impact that our lives had had on our little child.
